DNA Identification: Applications and Issues
Released: 2001-01-12T00:00:00

Introduction

As our understanding of human genetics has become more and more sophisticated, scientistshave developed increasingly powerful tools using genetic information to aid in identifying individualpeople. DNA can be helpful in many situations where identification is at question: For example,in criminal cases, forensic DNA evidence can link a suspect, or a weapon such as a knife, to a crimescene. It can also exclude a suspect. The best known sources of DNA evidence are blood andsemen, but increasingly it can be obtained from other items, such as a bottle cap, a toothbrush, a bitemark on a piece of cake, or a fragment of a contact lens. Another use is to identify human remains,such as of a soldier killed in battle. Or it might be used to determine biological relationship, suchas in paternity cases. This report focuses on using human DNA to determine individual identity, butanimal and plant DNA can also be used, to identify species (for example, did a sample of meat comefrom a protected whale species?) or even individuals (did a seed pod found in a truck come from aparticular tree at a crime scene?). (1)

Those and similar developments raise several policy issues, including the use of genetic information in the criminal justice system, the impacts of continuing technological improvements,and the effects of the technology on privacy and individual rights. This report provides an overviewof how genetic information is used in identification and some of the issues associated with thoseuses. It begins by discussing the unique properties of genetic information that make it a powerfultool for identification and what is involved in making identifications from physical evidence. Nextis a description of current federal programs and activities related to DNA identification, followedby discussion of issues raised by the development of this new technology. Legislation activity in the106th Congress focused on several criminal-justice issues; for detailed discussion, see CRS Report RL30694(pdf) , DNA Evidence: Legislative Initiatives in the 106th Congress .

Why DNA Can Be Used in Identification

The use of DNA in identification -- sometimes called DNA typing or DNA profiling (2) -- resultsfrom its unique characteristics. Those characteristics also affect how it can be used and the issuesthat arise from using it. Key features are described below.

It is a complex molecule, containing much information. DNA is a chemical, deoxyribonucleic acid, consisting of modular components, called nucleotides, that are connected in a linear sequence. Each nucleotide contains one of four bases -- called adenine, cytosine, guanine, and thymine, oftendesignated by their initials A, C, G, and T. Each DNA molecule consists of two complementarystrands, with each adenine on one strand paired with a thymine on the other, and each guanine witha cytosine. The sequence of bases strung along a DNA molecule contains the information that formsthe basis of the genetic code of humans and most other organisms. (3) Much of the growing body ofknowledge about DNA comes from efforts of the Human Genome Project, a major goal of whichis to create a map of the code and identify the sequence of bases on the DNA molecule. (4) DNAidentification technologies tap a small part of the large set of information that the molecule contains.

Each person has billions of identical copies of DNA in the cells of the body. Most of the billions of cells in a person's body contain identical sets of DNA molecules (5) -- approximately 3 billionbase-pairs per cell altogether. Most of the DNA is contained in 23 pairs of chromosomes in thenuclei of cells. Within each pair, one chromosome is inherited from the mother and the other fromthe father. Some DNA, inherited only from the mother, is also contained outside the cell nucleus,in structures called mitochondria, which are small bodies with many copies in each cell. Becausethe human body contains so many copies of DNA, even a very small amount of body fluids ortissues, such as blood or skin, can yield useful identifying information.

The structure of the molecule, and therefore the information it contains, varies from person to person. DNA sequences from any two people will be the same at many points along the DNAmolecule, but the overall nuclear DNA sequence of each person is unique, except for identical twins,who have identical DNA. (6) On a single chromosome,individual alleles, which are discretecomponents of a DNA sequence, are inherited intact. Each pair of chromosomes has many pairs ofalleles (7) (the total number is as yet unknown), withone member of the pair inherited from the fatherand the other from the mother. The region of a pair of chromosomes containing a pair of alleles iscalled a locus. The DNA of the two alleles inherited at any particular locus may have identical ordifferent base-pair sequences. (8) It is the substantialvariation in DNA among people that ischaracterized with the technologies used in DNA identification.

The structure is inherited, so the DNA of close relatives is more similar than that of distant relatives or unrelated people. Since half of a person's DNA comes from each parent, (9) full siblingsalso share half their alleles, on average, and grandparents and first cousins, one quarter. However,since a son receives his Y chromosome from his father, all the alleles on that chromosome areidentical to the father's and are inherited through the paternal line alone. (10) Similarly, all alleles inmitochondria are identical to the mother's and are inherited through the maternal line alone. (11) Therefore, the mitochondrial DNA of a male, for example, will be identical to that of his maternalgrandmother, and his Y-chromosome DNA identical to that of his paternal grandfather. Theinheritance patterns of DNA mean that analyzing a person's DNA can also provide identifyinginformation about a relative.

Most of a person's DNA has no known biological function. Genes are segments of DNA thatcontain the code for making specific chemicals (mostly proteins). Humans have tens of thousandsof genes (the exact number is not yet known), but they comprise only a small part of a person'sDNA, most of which has no known function. However, many nonfunctional segments of a person'sDNA can be characterized with the techniques of molecular biology; those segments are called markers . The distinction between genes and markers has implications for use in identification thatwill be discussed later.

DNA is easily preserved with the structure intact. DNA is a surprisingly stable chemical, and sequences can be easily preserved intact in dried or frozen samples. However, DNA can bedegraded, particularly in warm or moist environments or in the presence of many commonchemicals. The ability to use DNA in identification depends both on the size and the condition ofthe sample. That has consequences for sample collection, handling, and storage in applications suchas law enforcement.

How DNA Is Used in Identification

Using DNA in identification requires comparing DNA whose source has not been determined(such as from a crime scene or from a child in a paternity case) with DNA whose source is known(such as from a suspect or from a putative father). Four basic steps are involved: characterization,comparison, calculation, and interpretation. They are each discussed below, along with implicationsfor applications and issues.

Characterization

The first step is to characterize or profile corresponding DNA sequences in the samples to be compared. For forensic evidence in a criminal case, one or more samples of blood, semen, or othersources of DNA related to the crime will be processed, as will usually a sample from one or moresuspects. It is not possible with current technology to characterize the entire DNA sequence. Instead, alleles at specific loci are characterized. The technique used depends on the particular kindof marker. The major kinds of markers in use today are VNTRs, STRs, mtDNA, and certain simplersequences.

For most of the fifteen years during which DNA typing has been used in forensics, VNTRs (variable number of tandem repeats) have been the major kind of marker used. They have thegreatest potential power to identify or exclude, because they vary more from person to person thanany other DNA system used in identification. They consist of sections of DNA in which a sequenceof about 15-70 bases is repeated many times. Analysis of a sample using VNTRs measures theapproximate number of repetitions in each marker examined. That number varies substantially fromperson to person. Analysis of VNTRs uses RFLP (12) technology, which requires that substantiallymore DNA be present, and in good condition, in the sample than do the other systems describedbelow. Therefore, many samples that are degraded or have very small amounts of DNA cannot beprocessed using VNTRs.

STRs (short tandem repeats) also consist of repeated sequences, but the number of bases repeated is smaller (2-4), as is the total length of DNA comprising an allele (approximately 100-300bases for STRs versus 500-10,000 for VNTRs). STRs are not as variable as VNTRs, and thereforemore loci must be typed to obtain the same resolving power as with VNTRs. (13) Nevertheless, STRscan be examined with much smaller samples (for example, requiring a bloodstain the size of apinhead rather than one the size of a quarter coin), for two reasons. First, DNA-amplificationprocedures (known as PCR -- the polymerase chain reaction) can be used. The process uses theability of DNA to replicate itself to make many identical copies from a small initial amount of DNA. The procedure does not yet work with VNTRs. Second, because the sequences are shorter, they areless likely to be damaged if the sample is degraded. Therefore, such samples can often yield moreusable results with STRs than with VNTRs. STRs also have some other technical advantages overVNTRs. In particular, they can be processed in the laboratory much more quickly and they are easierto interpret. For those reasons, STRs, which first became available for forensic use a few years ago,are quickly replacing VNTRs as the standard marker for typing.

Mitochondrial DNA (mtDNA) can be used in even smaller or more degraded samples than STRs. That is because the relevant DNA sequences are moderately short (approximately 1,200 basesor less), there are thousands of copies per cell, and they can be amplified. This kind of DNA can beextracted even from skeletal remains and has been used, for example, in identifying the remains ofarmed forces personnel from conflicts as far back as World War II. (14) Because of the way it isinherited, mtDNA from remains must be compared with samples obtained from maternal relatives. Therefore, it cannot be used to distinguish among maternally related persons. Also, mtDNA is notas variable as STRs and VNTRs, and it is therefore not as powerful a tool for making positiveidentifications. It also takes much longer to analyze than STRs.

Some other nuclear DNA markers, such as DQA and Polymarker, are also used to aid in identification. Those consist of simpler DNA sequences than STRs or VNTRs. They can beamplified and require only small amounts of DNA, but they are less variable than STRs or VNTRs,and some of the loci used are closely linked to genes or are genes themselves. However, they canbe processed very rapidly and are often used to determine quickly whether a potential source of DNAshould be eliminated or investigated further using more sensitive marker systems. They are alsoused extensively in paternity cases.

Comparison

Once DNA from the samples is characterized, the resulting profiles are compared. If one or more alleles differ in the two samples, they are said not to match. In that case, if the analysis wasperformed correctly, the samples did not have the same origin. In the case of a criminal suspect, thatmeans that the suspect did not produce the DNA found in the evidence. In a paternity case, it meansthat the putative father was not the biological father. If an attempt is being made to identify remainsusing mtDNA, it means that the person whose remains were typed is not related to the supposedmaternal relatives. This use of DNA as a means of exclusion is a powerful and important use,particularly in the criminal justice system. A common estimate is that one-quarter of named suspectsare excluded in cases where DNA evidence is used. (15) Also, in the past few years, more than 60people convicted of violent crimes in the United States have been subsequently exonerated as a resultof DNA evidence. (16)

If the profiles match -- that is, if they are identical at every locus -- then they could have come from the same source. Alternatively, the source could be someone else who has an identical profilefor the markers that were examined. The way such a match is treated in DNA evidence has usuallybeen different than for other sources of identifying information, such as fingerprints. In the latter,a match has usually been considered either a positive identification or inconclusive -- for example,either the suspect left the fingerprints or could not be ruled out -- depending on the quality of theprint. For DNA, in contrast, the science of population genetics provides in many cases a way ofestimating quantitatively the chances that the DNA could have come from another source. Thechances of such a coincidental match depend on both the number of markers used and the variabilityexhibited by those markers. Therefore, results of DNA analysis have usually been given in termsof the probability that such a match could be coincidental rather than a conclusion about identity. (17)

Calculation

For several years, there was controversy about how best to perform calculations to estimate probabilities in DNA identification, but that issue is now largely, although not completely, settled. The specific procedures can be complex and will vary depending on the circumstances and thesystem used. However, there are two basic steps:

The population frequency of each allele in the profile -- that is, the percentage of people who have that allele in the population examined -- is identified. In most cases, those frequencies areestimates drawn from extensive data banks such as those compiled by the FBI. (18) Subpopulationswithin a country such as the United States vary in the frequencies of different alleles, and thereforecomparisons may be made to data from the most relevant subpopulation, usually a racial or linguisticgroup, or, if it is not known what group the source of DNA belonged to (as is often the case withDNA from crime scenes), from two or more subpopulations.

The frequencies are multiplied together, with the aid of appropriate mathematical formulas, to produce an estimated probability that someone drawn at random from the population would have thatprofile. If enough loci are used, those probabilities can be very small -- on the order of one chancein billions or even trillions -- even though the frequency of any given allele is likely to be on theorder of 1-10%.

In some cases, probability calculations may not be appropriate or useful. For some loci, the frequencies of alleles in the population as a whole might not be known, or there might be too fewloci or too few alleles at a locus to yield useful probability estimates. In such a case, a match meansthat a putative source cannot be excluded, but there might be many other potential sources. Or theparticular case might not require a calculation. For example, if the question is which of two menfathered a child, no calculation is necessary if the profile of one yields a match and the other doesnot. Or, in a case of identification of remains with mtDNA, it might be known that a soldier camefrom one of four families. If the maternal mtDNA profile of only one of the four yields a match, thenthe soldier came from that family. However, if more than one source produces a match in either ofthose two examples, then DNA evidence cannot resolve the question unless more loci can beexamined. Another situation that can present problems for making useful calculations is where DNAfrom more than one person is in the sample. In such mixed samples, if the DNA contributed bydifferent people cannot be separated, (19) then itmight only be possible to determine if someone canbe excluded.

Interpretation

There are two essential questions involved in interpreting the results of a DNA identification: Did the DNA come from the person (or family) who is thought to be its source, and what is thesignificance of the answer for the case at hand?

The probability calculation, when performed, is used to help answer the first question. If the probability estimate is low enough, the expert who provides it may declare a positive identification-- that the person in question was in fact the source of the DNA. (20) However, the question of whatprobability level (or other criterion) is required to ensure a positive DNA identification is not yetsettled, and in many cases, experts may be reluctant to make such a declaration, preferring to providesimply the probability estimate for the jury or other trier of fact to interpret. That is in contrast tothe situation with fingerprints, which are accepted as unique (even in identical twins, unlike DNA)but for which probabilities are not calculated. Fingerprints have been used effectively for muchlonger than DNA, so little question remains about how they can provide positive identification. Inaddition, they are not as amenable to statistical analysis as is DNA evidence, although that isbeginning to change as automated fingerprint analysis systems are developed and refined. However,with DNA, triers of fact may interpret a very low probability estimate as a positive identification,provided that there are no significant questions about how the evidence was handled, the quality ofthe laboratory analysis, or special circumstances of the case.

Once a positive identification has been made (or found very likely), its significance must be determined. That would seem straightforward but is not always. For example, in a rape caseinvolving DNA evidence, if the probability of a coincidental match is very small, that would bestrong evidence of a sexual encounter but would not of itself be proof of guilt, since the encountermight have been consensual. However unlikely, it is also possible, for example, that there was alaboratory error or even that blood or other sources of DNA might have been planted by someonewishing to frame a suspect. For those and other reasons, a match probability in a criminal caseshould not be interpreted as a probability of guilt. (21) However, it does provide evidence for the juryor judge to consider in determining whether the accused was the perpetrator of the crime.

Databases

Databases or indexes used in DNA identification are of three basic kinds. One provides theallele frequencies that are used in calculations to estimate profile frequencies and matchprobabilities. Such population databases are drawn from anonymous samples and are separated orstratified according to the population group (usually based on ethnicity or race) of the donors, sinceallele frequencies, and therefore match probabilities for different profiles, may differ among suchgroups. Sources are various, such as blood donors or medical patients. (22)

The second kind contains profiles of persons whose identity is known. One example is databases with STR or VNTR profiles of convicted felons or of victims of unsolved crimes (suchas the CODIS database system, discussed below). Another is databases with profiles of missingpersons or their biological relatives, such as mtDNA profiles of maternal relatives of armed forcespersonnel lost in past military conflicts (see below). When a profile is obtained from a relevantsample whose source is not known, the database can be searched to determine if a match, called a cold hit, is found. For example, in an increasing number of cases, a suspect is identified when aDNA profile from a crime-scene sample is searched against a database containing profiles of personsconvicted of violent crimes or other felonies.

The third kind of database contains profiles of persons whose identity is not known. Samples might come from crime scenes or unidentified remains. When a profile is obtained from a relevantsample whose source is known, the database can be searched for cold hits, as above. For example,a profile obtained from a suspect in another crime can be searched against a forensic database ofprofiles associated with crimes for which there are no suspects. In 1999, a DNA profile of a malemurdered in Florida was found to match DNA evidence from nine rapes, three in Florida and six inWashington, D.C. (23)

Federal Agency Programs and Activities

Federal agencies with significant involvement in DNA identification activities include theFederal Bureau of Investigation (FBI), the National Institute of Justice (NIJ), and the Bureau ofJustice Assistance (BJA) in the Department of Justice; the National Institute of Standards andTechnology (NIST) in the Department of Commerce; and the Armed Forces Institute of Pathology(AFIP), the Army Central Identification Laboratory, Hawaii (CILHI), and the Army CriminalInvestigation Laboratory (USACIL)in the Department of Defense. Major activities are describedbelow.

Federal Bureau of Investigation

Most forensic DNA evidence is developed and used by local or state law enforcement agencies. However, the FBI provides many important services to those agencies and is responsible forprocessing DNA evidence for cases under federal civilian jurisdiction.

FBI Laboratory. Major activities of the FBI Laboratory include training of federal, state, local, and foreign law enforcement and crime laboratorypersonnel; research and development in DNA typing technologies; development of an integratednational DNA database program; and providing expert testimony in the courts. (24) The laboratory wasthe first public crime laboratory in the United States to perform analysis of forensic DNA evidence,creating its DNA Analysis Unit in 1988. It is currently the only such laboratory performing mtDNAanalyses.

The laboratory also administers the Combined DNA Index System. CODIS is a distributed system of local, state, and national DNA databases that are linked electronically, permitting thecomparison of profiles stored in different locations. Begun as a pilot program in 1990, it wasauthorized in the DNA Identification Act of 1994 ( P.L. 103-322 ). More than 40 states nowparticipate. CODIS has several indexes. One, a convicted offenders index, contains DNA profilesof persons convicted of qualifying crimes. Current law does not specify qualifying federal crimes. However, section 811(b)(2) of the Antiterrorism and Effective Death Penalty Act of 1996 ( P.L.104-132 ) required that states, to be eligible for grants to improve their capacity to perform forensicDNA analyses and certain other activities, (25) collect DNA samples from persons convicted of sexualfelonies. All 50 states now require samples from such persons. Most also collect samples frompersons convicted of murder or other violent crimes, and several from those convicted of anyfelony. (26)

Other indexes are a forensic index, which contains profiles of DNA samples taken from crime scenes (especially from cases without any suspects); a population file, which contains informationon allele frequencies to be used in calculating match probabilities; and a missing persons indexcontaining profiles from unidentified remains.

The national component of CODIS, called NDIS, the National DNA Indexing System, has been in operation since 1998. Laboratories in 24 states currently contribute DNA profiles to NDIS. (27) While CODIS initially used VNTR markers, they are largely being replaced with the more powerfulSTRs (see section on sample backlogs below). NDIS uses thirteen core STR markers that have beenestablished as a standard set by the FBI.

DNA Advisory Board. DNA typing is technology intensive. That makes issues of quality control and assurance especially important. To help addresssuch issues, P.L. 103-322 required that the FBI Director establish a DNA Advisory Board (DAB)to recommend quality assurance standards for forensic DNA analysis. Following submission ofDAB recommendations, the director established standards effective October 1, 1998. They replacedstandards that had been established by the Technical Working Group on DNA Analysis Methods(TWGDAM), a practitioners' group representing federal, state, and local forensic laboratories andsupported by the FBI. As of 1998, most of the publicly funded crime laboratories in the UnitedStates followed DAB or TWGDAM standards, and about half were accredited by an officialorganization. (28) DAB is scheduled to dissolve atthe end of 2000, at which time its functions will betransferred to the renamed TWGDAM, now called the Scientific Working Group on DNA AnalysisMethods (SWGDAM).

National Institute of Justice

The National Institute of Justice (NIJ), a research agency within the Office of Justice Programs, engages in several kinds of activities related to DNA evidence. The institute supports research toimprove speed, reliability, and sensitivity of DNA profiling and to reduce its cost. There are threemain activities, administered through the NIJ Office of Science and Technology: the DNA Five YearResearch Program, the Forensic DNA Laboratory Improvement Program, and the NationalCommission on the Future of DNA Evidence. The DNA Five Year Research Program (1999-2003),is awarding $5 million per year to support research aimed at reducing the cost and time of processingDNA samples, developing technologies to enhance the reliability of DNA analysis and performanalyses at crime scenes, and developing standard test materials and new markers. (29)

The Forensic DNA Laboratory Improvement Program was initiated in FY1996 with DNA Identification Grants, authorized in P.L. 103-322 (Sec. 210302). Appropriations for the programhave grown annually (see table). From FY1996- FY1999, the program awarded grants to state andlocal governments, up to 75% of the total cost of the project, to develop and improve the abilitiesof forensic laboratories to analyze DNA evidence. In FY2000 and FY2001, funds were awardedunder a new series of grants authorized by the Crime Identification Technology Act of 1998 ( P.L.105-121 ), with half allocated by NIJ to the DNA Identification Program and half to the eliminationof sample backlogs (see below). That program can fund up to 90% of the total cost of a project. (30)

Appropriations for State and Local DNA Laboratory Support,FY1996-FY2001 (in millions of current dollars)

Note: FY2000 includes funds for addressing sample backlogs. Source: FY1996, P.L. 104-134 ;FY1997, 104-208; FY1998, P.L. 105-119 ; FY1999, P.L. 105-277 ; FY2000, P.L. 106-113 ; FY2001, P.L. 106-553 .

A 1996 NIJ-funded report (31) led Attorney General Reno to charter, in September 1997, theNational Commission on the Future of DNA Evidence (hereinafter called the DNA Commission). This four-year NIJ commission is examining several topics, including the postconviction use ofDNA, legal concerns, training and technical assistance, and future technological developments. Itsmembers include representatives from federal, state, and local law enforcement agencies, thejudiciary, defense lawyers, and other groups and areas of expertise. Rather than producing a singlefinal report, the commission is developing reports on specific issues and making recommendationson an ongoing basis. In 1998, the commission first identified the need for a special effort to addressa backlog of hundreds of thousands of DNA samples, taken from convicted persons and from crimescenes, that have not yet been processed (see section on sample backlogs below). (32) A 1999 report (33) recommended procedures for handling postconviction DNA-typing requests.

Bureau of Justice Assistance

The Bureau of Justice Assistance supports state and local criminal justice programs. It administers formula grants, including Byrne grants (42 U.S.C. 3751), which can be used, amongother purposes, to develop or improve the DNA-analysis capabilities of forensic laboratories; andState Identification Systems grants, which can be used, among other purposes, to help laboratoriesdevelop their capabilities with respect to CODIS. (34)

National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) has played a major role in the development of standards for DNA profiling, as part of its long-standing role in developingtechnological standards and measurements generally. (35) The standard reference materials that NISThas produced, both for VNTR and STR analysis, are used by laboratories to test the accuracy of theiranalyses. (36) They are therefore importantcomponents of quality-assurance and control activities. NIST also performs research on new DNA-typing technologies, both through the BiotechnologyDivision (within Scientific and Technical Research and Services) and the Advanced TechnologyProgram (within Industrial Technology Services). Many of the DNA-forensic activities in whichNIST engages are performed in collaboration with other agencies, such as the NIJ and Departmentof Defense, and with private industry.

Department of Defense

The two major uses of DNA identification by the Department of Defense (DOD) are in criminal investigation (see below) and in the identification of remains of military personnel. To aid in suchidentification, DOD established in 1988 the Office of the Armed Forces Medical Examiner withinthe Armed Forces Institute of Pathology, (37) underthe Assistant Secretary of Defense for HealthAffairs. DNA was first used to identify combat fatalities in 1991 in Operation Desert Storm. At thattime, the DNA Registry (38) was formed, consistingof two components. The Armed Forces Repositoryof Specimen Samples for the Identification of Remains (AFRSSIR) collects and stores DNA samplestaken from active duty and reserve personnel. (39) Armed Forces personnel are required to provideDNA samples for deposit in the repository. Currently, the repository holds more than 3 millionspecimens. When a casualty occurs that requires DNA identification, the Armed Forces DNAIdentification Laboratory (AFDIL) processes relevant samples to produce nuclear (STR and otherPCR-based systems) or mtDNA profiles. AFDIL also performs analyses of samples in other selectedcases. (40) Two examples of the latter are assistingthe FBI in identifying remains after the fire at theBranch Davidian compound in Waco, Texas, in 1993, and assisting the National TransportationSafety Board in identifying passengers who died in the crash of TWA Flight 800 in 1996.

Another DOD unit involved in DNA identification of remains is the United States Army Central Identification Laboratory, Hawaii (CILHI). (41) Thelaboratory recovers and identifies remains ofmilitary personnel lost in past conflicts and unaccounted for. AFDIL performs mtDNA analysis onthe recovered remains. AFDIL maintains a database of mtDNA profiles from maternal relatives whovolunteer to provide samples, for matching against profiles from remains. As of June 1999, 154matches had been obtained (including 112 from Vietnam and 34 from World War II). The mostprominent was the identification of First Lieutenant Michael J. Blassie, USAF, whose remains hadbeen interred in 1984 as the Vietnam Unknown in the Tomb of the Unknowns in Arlington NationalCemetery. Lt. Blassie had been lost in 1972 in Vietnam. Samples of mtDNA from maternalrelatives in seven families involved in the investigation were compared with mtDNA from a bonefragment taken from the tomb, and the samples from the Blassie family provided a very close match.

The United States Army Criminal Investigation Laboratory (USACIL) performs DNA analysis for criminal investigative agencies within the Department of Defense. The laboratory analyzesapproximately 500 cases per year and recently converted from VNTR to STR analysis using the 13core loci. USACIL participates in CODIS, providing profiles for NDIS of evidentiary samples forspecific cases and searching for matches in cases under investigation, where appropriate. However,the armed forces do not currently collect samples from convicted offenders (see the section belowon issues). USACIL works only on cases with a military connection. (42)

Other Agencies

Three other federal agencies support research that has contributed to the scientific basis for advances in DNA identification. The Office of Biological and Environmental Research, in theDepartment of Energy, and the National Institutes of Health, in the Department of Health and HumanServices, are the lead agencies for the Human Genome Project. They also support research onethical, legal, and social aspects of DNA identification and other applications of advances ingenomics. (43) The National Science Foundation,an independent agency, supports relevant basicresearch in molecular biology and in the social sciences at universities and other researchinstitutions. (44)

Relevant Public Laws

When DNA evidence first became available in the United States, questions often arose aboutthe quality of analyses and the absence of widely accepted standards. (45) Also, the typing of specimenswas expensive, (46) and its availability to many stateand local law enforcement agencies was thereforeuneven. The DNA Identification Act of 1994, a subtitle of the Violent Crime Control and LawEnforcement Act of 1994 ( P.L. 103-322 ), addressed quality control and privacy issues. It authorizedthe DNA Identification Grants program administered by NIJ (see above). The law authorizedappropriations for the program through FY2000. It also authorized use of Drug Control and SystemImprovement Grants for similar purposes (42 U.S.C. 3751; those grants are part of the Edward ByrneMemorial State and Local Law Enforcement Assistance Programs, or Byrne grants). The DNAIdentification Act required that forensic laboratories receiving the grants follow specified qualityassurance and privacy provisions. Recipients are to meet current quality-assurance standards, asspecified by the FBI director, and undergo regular proficiency testing in DNA analysis. The use ofDNA samples analyzed by recipients are restricted to use in law enforcement, judicial proceedings,and criminal defense. However, anonymized samples can also be used in population databases,research, and quality control activities.

The act also provided for the establishment of the FBI's DNA Advisory Board, to recommend quality-assurance and proficiency-testing standards to the director (Sec. 210303), and required thatFBI personnel engaging in DNA analysis undergo regular proficiency testing (Sec. 210305). It alsoauthorized the establishment of CODIS indexes containing profiles of persons convicted of crimesand samples recovered from crime scenes or unidentified remains (Sec. 210304). The ConsolidatedAppropriations Act of 2000 ( P.L. 106-113 ) additionally provided for an index of profiles from"samples voluntarily contributed from relatives of missing persons" (Sec. 120).

The Antiterrorism and Effective Death Penalty Act of 1996 ( P.L. 104-132 ) authorized the application of CODIS to federal crimes and those committed in the District of Columbia (Sec.811(a)(2)). It also authorized grants to state and local government for participation in CODIS. Tobe eligible, states must collect DNA samples from persons convicted of felony sex crimes (seeabove). Also, the National Institutes of Health Revitalization Act of 1993 ( P.L. 103-43 ) establishedas one of the purposes of the National Human Genome Research Institute "reviewing and fundingproposals to address the ethical and legal issues associated with the genome project."

The Crime Identification Technology Act of 1998 ( P.L. 105-521 , 112 Stat. 1871) established the State Grant Program for Criminal Justice Identification, Information, and Communication. Grants can be awarded for a broad range of activities to, among other things, improve statecapabilities in crime identification and promote compatibility and integration among local, state, andfederal identification systems, and including accreditation and certification programs relating toDNA analysis. Funding is authorized through FY2003.

Current and Emerging Issues

Some of the issues discussed below, particularly those related to law enforcement, were thesubject of legislation in the 106th Congress. See CRS Report RL30694(pdf) for a discussion of thoselegislative initiatives.

Law Enforcement and Criminal Justice

Sample Backlogs. DNA samples are now collected in all 50 states from persons convicted of certain crimes. Also, DNA evidence is routinelygathered from crime scenes and victims in cases of rape, murder, and other violent crimes. As DNAtechnology has improved and states have increased its scope in criminal justice activities (see nextsection), the workload in forensic laboratories has increased. For example, from 1996 to 1997,casework increased 40%, from a total of about 15,000 to 21,000, and convicted-offender samplesincreased more than 60%, from 72,000 to 116,000. (47) Given limited resources, forensic laboratoriesmust prioritize the analysis of those and other samples they receive. Therefore, many samples, suchas from scenes of crimes for which there are no suspects, and from convicts who are not suspects foradditional crimes, are given lower priority. Currently, there is a backlog in the United States ofseveral hundred thousand such samples that have not been analyzed and entered into CODISdatabases. That means that profiles from those samples are not available for database searches. Given that "cold hits" have been identified through such searches, the DNA Commission and othershave proposed that funding be increased to process that backlog. Also, the $30 million appropriatedby Congress in FY2000 for DNA grants included funding for processing backlogged samples.

An additional factor is the conversion of existing profiles from VNTRs to STRs. Some states have not converted to using the core STR markers, and profiles that use other markers cannot besearched against NDIS or CODIS STR records. Conversion requires that a DNA sample be retyped-- reanalyzed with STR technology. More than 200,000 existing profiles may need such retyping. Also, there are many "owed" samples -- that is, samples that can be taken under existing law buthave not been. Those include many paroled or released convicts. The number of such owed samplesnationwide may exceed the number currently backlogged. (48)

Failure to process backlogs may have several consequences. Crimes that might be solved with the help of a database match may remain unsolved. That is of particular concern in cases where aperpetrator is likely to perform additional crimes, or where a database match would prevent aninnocent person from being wrongly suspected or perhaps even charged with the crime. Also,crime-scene samples from unsolved crimes may eventually be destroyed as statutes of limitationsexpire, permanently eliminating any possibility of typing any DNA evidence.

The size of the backlog makes the question of prioritization particularly important, but it is not straightforward. For example, typing a person's DNA is usually much less expensive than typingDNA from a crime scene, because in the latter case, several samples must usually be processed and,unlike with convicted-offender samples, processing cannot usually be automated with existingtechnology. That might suggest that the highest priority should be given to typing convicted persons,since many more samples could be processed per dollar invested. However, to make a successfulcold hit requires that crime-scene samples also be typed, so that they can be compared with theprofiles of convicted persons. Also, logistically, it is often easier to obtain a sample from someonenewly in custody than from someone who has been released. However, a person while in prison isnot a threat to the community, whereas someone who has been released might be; nevertheless, aprisoner might be discovered through DNA analysis to have committed other crimes before havingbeen imprisoned. Finally, solving old crimes with the help of DNA evidence serves justice andmight help prevent future crimes, but it might also have negative consequences. For example,reopening a case that is several years old might retraumatize victims or their families who haveworked to recover from the effects of the crime.

Additional federal funding to help reduce the backlog could substantially increase the speed with which backlogged samples are processed, easing uncertainties about how best to prioritize thesamples and increasing the rate at which crimes are solved. Also, the existence of the backlog couldbe attributed in part to the success of the DNA Identification Act grant program, and thegrant-eligibility requirements in the Antiterrorism and Effective Death Penalty Act of 1996 discussedabove. In addition, the processing of backlogs would have benefits across states, especially withrespect to "travelling offenders" who commit crimes in more than one state.

Databases. A central issue relating to the kinds of crimes for which DNA is collected from convicted persons for inclusion in a profile database orindex. States vary in the crimes for which they collect DNA samples. Qualifying offenses include,at a minimum, felony sex crimes, but several others are included by different states: offenses againstchildren (40 states), murder (36), assault and battery (27), kidnapping (22), robbery (19), burglary(14), and all felonies (6). Also, 24 states collect samples from juveniles convicted of qualifyingoffenses, most collect retroactively from incarcerated convicts, and some collect from thosepreviously paroled or on probation. (49) In theUnited Kingdom, the Forensic Science Service, anexecutive agency of the Home Office, maintains a national database with DNA profiles of "suspectscharged, reported, cautioned or convicted for a recordable offence," which is any crime punishableby imprisonment, plus certain other specified offenses. (50) Profiles are removed if a suspect isexonerated or acquitted. As of July 2000, the U.K. database held approximately 700,000 profilesand had yielded more than 77,000 matches of suspects to crime scenes since its inception in 1995,with almost 130,000 profiles removed following acquittal. (51)

In determining whether to broaden the range of qualifying crimes, questions might be raised such as the following: What is the cost-effectiveness of profiling those convicted of a particularclass of crime? For example, are the resources needed to profile those convicted of nonviolentcrimes more effective if spent on profiles or on other aspects of crime solving and prevention? (52) What is the proper balance between using profiles to help protect citizens from crime, on the onehand, and the need to protect the civil liberties and privacy of those who might be subject toprofiling, on the other? The power of DNA evidence has led some to call for indexing profiles ofall arrestees, or even of all citizens at birth, while others have raised concerns about the effects ofsuch measures on civil liberties. (53)

Postconviction Analysis. A powerful use of DNA evidence is in exonerating the innocent, including in some cases where people have been wrongfullyconvicted. Several issues are associated with postconviction DNA analysis. Among them are whensuch procedures are appropriate, and what is the proper role of the federal government.

There are several potential reasons why DNA analysis might not have been done when a case was first prosecuted. One is that the identity of the suspect might not have been an issue at the trial-- for example, the involvement of a suspect in a sexual encounter might not have been in question,but rather whether the encounter was consensual. In such a case, DNA evidence would probably notbe relevant. Another possibility is that no DNA evidence was found at the time, but turned up later. A third is that there was DNA evidence, but the technology to analyze it was not available when thecase was prosecuted. The first use of DNA typing in the United States was in the late 1980s, andit was not widely available until a few years ago.

In some cases, relevant DNA evidence might have been found and analyzed at the time of the original prosecution but yielded inconclusive results because of the limitations of the technology atthe time. The much more sensitive STR technology did not become an established standard untilthe late 1990s, and many states still use the older, less sensitive VNTR markers. STRs or thepotentially even more sensitive (but less powerful) mtDNA can provide useful profiles from muchsmaller or more degraded samples than VNTRs. Consequently, an analysis that was inconclusivewith VNTR technology could lead to either a definitive exclusion or, alternatively, a strong matchif a more sensitive system is used. Improvements in DNA technology are likely to continue into thefuture, potentially making even more samples amenable to typing.

Most states currently do not permit new trials, based on newly discovered evidence, more thanthree years after conviction. (54) However, DNAevidence, properly handled, is very stable and canoften provide useful information even ten years or more after it was initially deposited. (55) Thisconfluence of advances in the technology, the stability of DNA evidence, and its strong and growingexclusionary power raise questions such as whether the time limit should be extended for caseswhere DNA evidence newly discovered or analyzed can be probative, and whether postconvictionlegal procedures should be changed to accommodate the particular features presented by DNAevidence. (56)

To date, a few states have passed laws that specifically permit postconviction DNA analysis for convicted persons claiming actual innocence. In considering proposed federal legislation, Congressmay consider questions including the following: Should such legislation apply only to crimes underfederal jurisdiction, or should it also apply to states? What evidence standards should a petitionerbe required to meet for the procedure to be permitted? Should there be a requirement for evidenceto be preserved beyond exhaustion of appeals, and if so, for how long should it be preserved? Underwhat circumstances should elimination samples from victims or other third parties be required?What, if any, accommodation should be made for retyping when new advances are made in DNAtechnology? Should the government pay for analysis requested by an indigent inmate? Shouldwrongfully convicted persons receive compensation? (57)

Paternity Challenges

As more powerful DNA-typing techniques have become more affordable, their use in paternity analysis has grown. An emerging issue involves cases where men who have legally acknowledgedpaternity, sometimes for several years, are shown by DNA typing not to be the father of the child. A central question is whether the men in such cases, who may claim not to be responsible for childsupport since they are not the child's biological father, should nevertheless continue to be heldresponsible. A concern of child advocates is the potentially negative impacts on children if suchchallenges are allowed. States have varied in their treatment of this issue. (58)

Future Directions of the Technology

Current research on improving DNA identification is performed or supported mainly by NIST, NIJ, the FBI Laboratory, AFDIL, and private industry. Such research has several broad goals. Improvements in sensitivity of analyses would make useful typing possible from even smaller ormore highly degraded samples than at present. That could permit more powerful identification (orexclusion) from DNA in trace evidence from, for example, saliva, tears, and skin cells. Coupledwith further improvements in specificity, such as via use of a larger set of markers, it would alsoincrease the ability of DNA evidence to make positive or unique identifications. Even identicaltwins possess minor genetic differences that could eventually be detected. Reducing the timerequired to complete typing could lead to more timely following of leads as well as more quicklyremoving from further consideration those persons excluded by the evidence. As the costs ofperforming DNA analysis has come down, its use has increased. Further reducing cost would makeuse of DNA identification more widely available. Research on automation and miniaturization ofthe typing process may lead to cost reductions and further improvements in quality control. Conceivably, an automated, portable DNA-typing system could eventually be developed that wouldpermit on-site analysis and identification through comparison against a database via wirelesscommunication.

Such major improvements in the technology will take several years at least to perfect. It is generally believed that STR markers will remain the standard for DNA identification over the nextdecade, with mtDNA increasingly used to analyze highly degraded samples. Research to developways to amplify longer sequences may, however, lead to more use of VNTR or other more variablesystems in the near future. Also, the Human Genome Project and related efforts are increasinglyidentifying very small genetic differences, even at the level of a single base (single nucleotidepolymorphisms, or SNPs). Such research may lead to eventual development of better markersystems. In some cases, relevant physical characteristics, such as for eye color, might even bededucible from genetic sequences and could help, for example, in identifying suspects. (59)

There are several challenges raised by the likely future improvements in DNA typing. Improvements in forensic typing will need to be validated by the scientific and law enforcementcommunities and accepted by the courts before they become widely available for use in cases. Therefore, any given case is likely to involve technologies that are technically sound but not the mostrecently developed. Furthermore, significant pressures exist to maintain a substantial degree ofstability in the systems used. Not only is adopting a new technology costly, but frequent change canlead to longer and more costly proceedings and to uncertainty about the most appropriate approach. (60) One concern raised is that technological advances could lead to a lengthening of the appeals processin cases involving DNA evidence, or a flood of postconviction petitions for typing or retyping insituations where it would not actually be helpful. Such concerns will need to be balanced againstwhatever added ability the advances provide in reversing or avoiding wrongful convictions.

As the power of DNA profiling to identify a person continues to improve, the question arises, can a person be positively or uniquely identified from a DNA profile? FBI experts will currentlytestify that a person is the source of a DNA sample, provided that the match probability is lowenough (see the section on interpretation of DNA evidence above). However, it has not yet beensettled generally what probability, or alternatively how many loci, are needed to effectively eliminatethe possibility that a match could be coincidental. One complication is that match probabilities donot take into account the possibility of misidentification resulting from errors at the laboratory or inthe evidence custody chain. Both experts and the courts have generally agreed that such possibilitiesare best addressed in other ways. (61)

The stability of DNA evidence makes it potentially useful not only in postconviction typing; it also raises the question of whether statutes of limitations should be extended for crimes in whichsuch evidence is potentially important. That question will likely increase in importance as thenumber of DNA profiles from "cold cases" grows in databases and indexes such as CODIS. Thebenefits of using DNA evidence to bring effective prosecutions after a longer period than currentlyfeasible will need to be balanced against factors such as the desire to avoid retraumatizing victimswho have recovered from the effects of crimes and the need to prioritize the use of limitedlaw-enforcement resources. (62)

Relationship of DNA Identification to Medical Genetic Testing

Both similarities and differences exist between the use of DNA for identification and for medical genetic tests -- with respect to techniques, applications, and the issues raised. The mostfundamental similarity is that both rely on genetic differences among people. The most fundamentaldifference is in the characteristics of the DNA sequences that each currently uses -- in particular,variability, functionality, and independence.

Variability. A genetic marker used in identification should be highly variable -- that is, there should be many alleles, and none of them should be very common. The more variable the markers,the fewer are needed for a positive identification. In contrast, a gene examined in a genetic test isunlikely to be highly variable. That is because genetic tests are most often used in medicine, todiagnose or predict the likelihood of a disease or condition caused by a genetic abnormality, whichmost people will not have. (63)

Independence refers to whether different loci tend to be inherited together. Two loci that occur close together on a chromosome will usually tend to be inherited together -- they will be linked, notindependent. Two loci that occur on different chromosomes will usually be inherited independently-- they will be unlinked. In genetic testing, only one locus is usually of interest, so linkage is notusually important. In contrast, use of DNA to identify people requires examining several loci, andthe mathematics that is used works best if the loci are independent. (64)

Functionality. A sequence is of interest in genetic testing specifically because it is a gene that codes for a particular chemical product. However, in identification, a noncoding sequence or markeris of most interest. (65) That is because themathematics that is used in identification works best withnoncoding loci. (66) Although most loci used inidentification are noncoding, it is possible thatfunctions for at least some will be discovered in the future. Furthermore, some, in particular STRs,are thought to be linked to coding loci that may be implicated in genetic diseases or conditions. (67)

Regulation and accreditation of laboratories performing medical genetic tests and DNA identification are accomplished through different mechanisms. Clinical laboratories, which mayperform medical genetic tests, are regulated and must be certified by the U.S. Department of Healthand Human Services through the provisions of the Clinical Laboratory Improvement Amendmentsof 1988, as amended ( P.L. 100-578 ). Standards are developed by the Health Care FinanceAdministration and the Centers for Disease Control and Prevention. Medical research laboratories,if they are supported by federal funds or are otherwise subject to regulation, are subject to federalpolicies relating to the protection of human subjects (45 C.F.R. 46, 21 C.F.R. 50 and 56). Forensiclaboratories do not require federal certification, but to be eligible for DNA Identification Grants orByrne Grants, they must adhere to standards set by the FBI and undergo regular proficiency testing( P.L. 103-322 , Sec. 210302). Also, in criminal and civil cases, DNA evidence must pass the scrutinyof the judicial process, where custody-chain and quality-control procedures, as well as other aspectsof typing, may be challenged. (68) Consequently,new DNA technologies are likely to be adopted moreslowly for forensic use than for medical testing.

Privacy and Discrimination

There is currently no federal law governing genetic privacy and discrimination per se, although Congress has considered several bills addressing such concerns from a medical perspective. Theexecutive branch has also taken some actions, as have several states. (69) The Privacy Act of 1974 (5U.S.C. 552a) places restrictions on agencies with respect to the disclosure of personally identifiableinformation in their possession, including any "identifying particular assigned to the individual, suchas a finger or voice print or a photograph." However, it applies only to federal agencies. ExecutiveOrder 13145 prohibits genetic discrimination against executive branch employees; it applies tomedical genetic tests and does not cover the use of DNA in identification per se. Other federal lawsand guidelines provide privacy protections for certain other kinds of personal information relatingto health and medical research. (70)

Current federal and state laws also provide safeguards against the misuse of DNA profiles collected in law enforcement. Specifically, the DNA Identification Act of 1994 ( P.L. 103-322 )required grantees to certify that DNA samples and analyses "be made available only --

(A) to criminal justice agencies for law enforcement identification purposes;

(B) in judicialproceedings, if otherwise admissible pursuant to applicable statutes orrules;

(C) for criminal defense purposes, to a defendant, whoshall have access to samples and analyses performed in connection with the case in which thedefendant is charged; or

(D) if personally identifiable information is removed,for a population statistics database, for identification research and protocol development purposes,or for quality control purposesï¿½.

The act also applies those privacy requirements to federal, state, and local participants in CODIS. However, state laws vary with respect to how such samples can be used. Somedisagreement exists over whether state protections are adequate. (71)

Samples deposited in the Armed Forces Repository of Specimen Samples for the Identification of Remains are limited to the following uses: "Identification of human remains; ï¿½[i]nternal qualityassurance activitiesï¿½; [a] purpose for which the donorï¿½ (or surviving next-of-kin) providesconsent;" or, when specifically authorized, criminal procedures for which "[n]o reasonablealternative means for obtaining a specimen for DNA profile analysis is availableï¿½." (DODD5154.24, Sec. 3.5).

Since most genetic markers currently used in DNA identification are noncoding, the privacy and discrimination issues raised are somewhat different than with medical genetic testing. Forexample, knowing someone's DNA profile for the 13 core STR loci can provide information aboutpaternity but provides no information at this time about physical traits such as a propensity to aparticular genetic disease. (72) However, the issuesmay begin to converge as new advances ingenomics are developed and applied, or if current identification technologies are applied in thecontext of genetic testing. For example, in some cases clinical research laboratories have reportedlyused STR typing of samples as an added protection against the possibility of potential mislabeling.

More generally, as DNA identification becomes more sophisticated, its potential applications are likely to broaden, potentially increasing privacy concerns. For example, it is already possible forparents to purchase kits for obtaining DNA samples from their children and to have profilesdeveloped from those samples and placed in a database to be used potentially if the children becomemissing. Such private-sector practices are not covered by federal laws and judicial rulings thatprovide privacy or other protections against misuse or abuse of the information.

Government agencies in other countries have also become involved in DNA-identification activities that would likely be limited to the private sector in the United States. Britain's ForensicScience Service (FSS) is an executive agency of the British Government but is permitted to operateas a nonprofit corporation that offers services not only to the government but also to the public. Among its services to corporations is the development of DNA profiles of employees who might beat risk of being kidnapped. The profiles could then be compared to any biological material providedby kidnappers. FSS also provides paternity-analysis services to the public. (73) The privacy of geneticinformation obtained or used in such services would presumably be protected by a European Uniondirective on privacy of personal data. (74)

Such broadening applications may raise concerns about "function creep," (75) the gradual wideningof an application to uses not originally intended. One example often given is the slowly broadeningrange of uses over the years of Social Security numbers. The identifying power of DNA, thedecreasing cost of typing, and the increasing ability to obtain a useful sample without drawing blood,make DNA potentially attractive for a wide range of uses requiring verification of identity. (76)

As long as DNA typing uses noncoding loci, privacy issues arising from its use in identification should remain limited. However, three potential issues might deserve particular attention as the useof the technology increases. First, as genomic research leads to increasingly sophisticatedtechnologies for detecting genetic differences, it may become possible to use coding loci (genes) toprovide identification. Use of coding DNA for identification could raise issues of privacy anddiscrimination similar to those that have raised concerns with respect to medical testing -- if, forexample, such information became publicly available during a judicial proceeding.

Second, DNA samples obtained from a person -- and in many cases from crime-scene evidence, remains, or other sources -- contain the person's entire genetic code, not just the profileinformation. Therefore, the disposition of the samples themselves, after profiling, is potentially anissue. That is especially a potential concern with respect to private-sector activities wheredisposition of profiles or samples is not necessarily regulated by current law. A case involvingelectronic commerce illustrates the concern. Toysmart.com collected information about customersunder a privacy policy that claimed the information would not be shared with third parties. However, when the company filed for bankruptcy, it included the database of customer informationamong the assets it was selling. The Federal Trade Commission unsuccessfully opposed the sale ofthe database. (77)

Third, a DNA sample and profile contain information not only about the subject, but also about that person's biological relatives. Therefore, consideration of privacy issues related to DNAidentification, as with genetic testing in medicine, must take into account potential impacts on familymembers. That can raise potentially difficult issues, as illustrated by the following hypotheticalexample. Suppose that a DNA profile from a convicted offender is similar but not identical to thatobtained from a crime scene. Is it appropriate based on that information for a sibling of theconvicted offender to be arrested as a suspect? Alternatively, suppose that a person is suspected ofcommitting a crime but there is insufficient evidence to make an arrest. Suppose further that theperson has a sibling who has a profile in CODIS. Is it appropriate to examine the profile of thesibling to determine how similar it is to the crime-scene evidence? Such examples are likely to arisein real cases as DNA becomes more widely used in identification. (78)

The growing use of DNA as an effective identification tool, and its increasing overlap with aspects of medical genetic testing, are likely to create a range of policy challenges over the nextseveral years. While this report has discussed several current and emerging issues, new ones maywell develop as the technology evolves. The biological role of DNA, the information it containsabout family members, and other features of the molecule and the technology may make some ofthose issues, and the appropriate legislative response, especially challenging.