U.S. flag
      An official website of the United States government, Department of Justice.
        Here's how you know
      Here's how you know**Official websites use .gov**
            
            A **.gov** website belongs to an official government organization in the United States.
      **Secure .gov websites use HTTPS**
            
            A **lock** (
            A locked padlock
            ) or **https://** means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. Menu

      
        close

            
            
                                              About NIJ
        
                    
  
          About NIJ
      
    
          The NIJ Director
          How NIJ Is Organized
          Mission and Guiding Principles
          Research and Development Process
          Strategic Framework
          Assessments of NIJ
          Annual Reports & Reports to Congress
          Staff Directory
          Funding & Awards
        
                    
  
          Funding & Awards
      
    
          Current Funding
          Forthcoming Funding
          Expired Funding
          Awards: Listing of Funded Projects
          Guidance for Applicants and Awardees
          Fellowship & Student Programs
          Travel Scholarships
          NIJ Challenge Program
          Library & Multimedia
        
                    
  
          Library & Multimedia
      
    
          NIJ Journal
          Podcasts
          Publications Listing
          Multimedia Listing
          Rated Practices on CrimeSolutions
          Rated Programs on CrimeSolutions
          Software & Databases
          Datasets
          Patents
          Topics
        
                    
  
          Topics
      
    
          Article Listing
          Corrections
          Courts
          Crime Prevention
          Crimes
          Drugs and Crime
          Equipment and Technology
          Forensic Sciences
          Youth Justice
          Justice System Reform
          Law Enforcement
          Tribal Crime and Justice
          Victims of Crime
          Events
        
                    
  
          Events
      
    
          NIJ 2024 Research Conference
          Scheduled Events
          On-Demand Events
          Research Meetings & Workshops
          NIJ-Hosted Online Training

                            
                                About
          Contact Us
          Subscribe
          Topics A-Z
                  Share
FacebookXLinkedInRedditPinterestEmail Home
 Animation demonstrating how DNA mixtures at a crime scene can occur.

August 5, 2020
Review the YouTube Terms of Service and the Google Privacy Policy
See reuse policy
  
  
          Transcript
0:01 Commonly, evidence found at a crime scene  will not have just one person's DNA on it,

0:06 but will instead have a mixture of  DNA from more than one contributor.

0:10 These mixtures are most commonly encountered in  sexual assault evidence but frequently occur in

0:15 other types of cases as well. This animation  will show step-by-step a sample murder case

0:21 that demonstrates just one example of how multiple  individuals DNA can end up on a piece of evidence.

0:29 Event One: the homicide victim borrows her  boyfriend's sweaty, dirty shirt to wear while

0:35 cleaning the house residual traces of his DNA  remain in the shirt from when he last wore it.

0:44 Event Two: while working, the victim wiped  sweat from her brow with the sleeve of her shirt

0:50 transferring some of her own DNA in the process.

0:57 At this point, multiple people have left  their genetic material on the shirt,

1:01 causing a mixture of DNA.

1:06 Event Three: a stranger breaks into  the house and encounters the victim,

1:10 who grabs a kitchen knife to defend herself;  through an ensuing struggle the victim cuts

1:15 the perpetrator some of whose blood  lands on the sleeve of the shirt.

1:25 Event Four: the intruder succeeds in wrestling the  knife away from the victim and stabs her with it;

1:31 the area surrounding her wound will have too  much of her own blood to provide a useful

1:35 sample of anything else, so investigators  will have to test other areas of the shirt.

1:44 Event Five: the victim's roommate arrives  home and startles the perpetrator.

1:49 She too struggles with the intruder who is still  holding the knife; the roommate sustains defensive

1:55 wounds to the hands and forearms but is not  killed. The perpetrator ends up fleeing the scene.

2:04 Event Six: after the perpetrator has left,  the roommate goes over to check on the victim.

2:10 Upon placing her lacerated hand on the victim's

2:12 arm the roommate transfers her own blood to the shirt sleeve.

2:21 When the shirt arrives at the lab and is analyzed by the technician, four different sets of DNA will

2:26 show up together on the sleeve. More clues will be necessary in order for the lab technician to

2:32 be able to sort out the combined DNA and determine who the four contributors were.
    
  
Disclaimer:
              Opinions or points of view expressed in these recordings represent those of the speakers and do not necessarily represent the official position or policies of the U.S. Department of Justice. Any commercial products and manufacturers discussed in these recordings are presented for informational purposes only and do not constitute product approval or endorsement by the U.S. Department of Justice.
  
Date Published: August 5, 2020
    
          Side navigation
  

        

  
  
              NIJ Journal
    
      
            
            
            
      Podcasts
    
      
            
            
            
      Publications Listing
    
      
            
            
            
      Multimedia Listing
    
      
            
            
            
      Rated Practices on CrimeSolutions
    
      
            
            
            
      Rated Programs on CrimeSolutions
    
      
            
            
            
      Software & Databases
    
      
            
            
            
      Datasets
    
      
            
            
            
      Patents
 Top

      National Institute of Justice

        
        
                        About NIJ
                    About NIJ
      
    
                  How NIJ Is Organized
      
    
                  NIJ Director
      
    
                  Research Disclaimer
      
    
                  Funding & Awards
                    Funding & Awards Home
      
    
                  Awards Listing
      
    
                  Current Funding
      
    
                  Guidance for Applicants and Awardees
      
    
                  Resources
                    Events
      
    
                  Podcasts
      
    
                  Publications
      
    
                  Topics
      
    
                  Multimedia
      
    
                  Reuse Policy
      
    
                  Contacts
                    Contact NIJ
      
    
                  Staff Directory
      
    
                  Submit a FOIA Request
      
    
                  File a Civil Rights ComplaintFacebook
          
                      X
          
                      YouTube
  

      810 7th St. NW, Washington, D.C. 20531
      
              Secondary Footer link menu
            Accessibility
              Plain Language
              Privacy Policy
              Legal Policies and Disclaimer
              No FEAR Act
              Freedom of Information Act
              USA.gov
              Justice.gov