Abstract:
The present invention comprises a method for detecting and analyzing forensic evidence. A digital image is taken of background radiation from a suspected-evidence area suspected to contain evidence. The suspected-evidence area is exposed to a high-intensity pulse of ultraviolet radiation. Another digital image is taken of fluorescence within the exposed suspected-evidence area. The digital images are processed to create a composite digital image showing regions of evidence. The composite digital image is analyzed to determine the wavelength of fluorescent radiation emitted by the regions of evidence. Composite evidence image and the analysis results are displayed. The present invention also comprises a forensic evidence detection and analysis system that includes a digital camera, an ultraviolet light source, a computer and display, and a computer program installed on the computer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for detecting and analyzing forensic evidence from an examined surface. 
     BACKGROUND OF THE INVENTION 
     In the field of forensic science, criminal investigators are seeking improved methods to detect evidence. Such evidence includes blood, saliva, semen, and other body fluids; as well as hair, flesh, bone fragments, teeth, human skin damage such as bruises, bite marks or cuts; shoe prints, fingerprints, footprints, tire prints, gunpowder residue, bullets, explosives, chemical and biological agents, paint, grease or oil, glass fragments, fibers and various trace evidence, including the alteration of documents. 
     The detection of evidence has historically been a combined process of art and science. One conventional method of obtaining, for example, fingerprint evidence is the careful lifting of fingerprints by applying a fine dust to the surface of a fresh print and then transferring the dust pattern onto a second surface. Fingerprint dusting powders were initially selected for their color contrasting qualities. Extremely fine fluorescent dusting powders were also used to visualize minute etchings of a surface caused by the breakdown of amino acids contained in fingerprint oils. The fluorescent dusting powder adheres to the etchings and reveals the fingerprint pattern upon illumination by ultraviolet radiation. Other substances, such as blood, saliva or semen, are easily detected where visible stains exist. However, often such revealing evidence is concealed from ordinary inspection via cleansing agents or even the passage of time. 
     In more recent years, ultraviolet light has been used by forensic specialists to aid in the viewing of otherwise invisible evidence. Ultraviolet (“UV”) radiation is light that is just beyond the visible spectrum. Whereas visible light has a wavelength ranging from about 400 nm to about 750 nm, UV radiation has a shorter wavelength and ranges from about 10 nm to about 400 nm. Although the unaided human eye cannot discern UV radiation, its presence can be shown by use of either UV-sensitive media or the resultant fluorescence of a UV-sensitive material. When fingerprints are dusted with fluorescent dusting powders, applied UV radiation will result in the fluorescing of the dusting powder, effectively making the fingerprints visible to the unaided eye. Other organic substances, such as saliva or semen, naturally fluoresce, and are thus also visible upon exposure to UV radiation. 
     Conventional UV fluorescence detection methods involve using a so called “black light” in the form of a continuous or non-flash flood-type UV source to continuously generate UV radiation near the evidence, and then using a camera with a filtered lens to capture the resultant fluorescent image onto film. Because the evidence will fluoresce at a relatively low intensity, light sensitive film and a relatively slow shutter speed are required. Additionally, the camera must also be held very close to the evidence. The effect, then, is a relatively narrow field scan that must be repeated many times to effectively detect evidence over a large area. 
     Variations on conventional UV fluorescence detection methods include the use of chemical reagents or vapors to deposit fluorescence-emitting particles onto fingerprint etchings where regular dusting methods are not appropriate. A laser, instead of a black light, may also be used to excite the fluorescence-emitting material. However, laser excitation is, by its very nature, limited to use over a small overall area. Additionally, the portability and use of a laser in small areas may be limited due to the large power supply required for operation of the laser. 
     A more recent UV detection method utilizes UV reflectance instead of fluorescence. Although the reflected UV detection method may not result in the clean images produced by UV fluorescence, high-intensity short-wave UV reflectance can reveal otherwise undetectable or difficult to detect evidence on non-porous surfaces that limit the use of fluorescent dusts or dyes. 
     Analysis of evidence detected through UV fluorescence or reflectance generally includes the development and close examination of photographs taken of the UV-detected evidence to determine the exact locations of the evidence. Dimensions of the detected evidence and overall shape are often obtained by hand measurement or even sketched reproduction. The substance of the evidence is determined by DNA testing as well as by other tests for specific reagents. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a method and system for detecting and analyzing forensic evidence. In one embodiment of the present invention, a method for detecting and analyzing forensic evidence is provided. A background fluorescence image of a suspected-evidence area is digitally captured. The suspected-evidence area is exposed to a pulse of ultraviolet radiation and an evidence-exposing fluorescence image of the suspected-evidence area is digitally captured. The background fluorescence image and the evidence-exposing fluorescence image are processed to create a composite evidence image. The composite evidence image is analyzed to determine one or more fluorescing wavelengths emanating from a corresponding one or more evidence regions within the suspected-evidence area. The composite evidence image and analysis results are displayed for evaluation. 
     In another embodiment of the present invention, a forensic evidence detection and analysis system is provided. The system includes a digital camera and an ultraviolet light source configured to pulse high-intensity ultraviolet radiation. A computer and display are also provided for processing and controlling the capturing of the images according to a computer program installed on the computer. The computer program is configured to process and analyze fluorescent images of an area illuminated by the ultraviolet light source and as captured by the digital camera. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings in which: 
         FIG. 1  is a simplified diagram of a combined forensic evidence detection and analysis system, in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic diagram of a combined forensic evidence detection and analysis system in accordance with an embodiment of the present invention; 
         FIG. 3  shows a forensic evidence detection system, in accordance with an embodiment of the present invention; and 
         FIG. 4  is an exemplary display device, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described by reference to the associated drawing figures. Identical labels and numbers in multiple drawing figures are meant to represent the same elements in each drawing figure. 
       FIG. 1  is a simplified diagram and  FIG. 2  is a schematic diagram of a combined forensic evidence detection and analysis system  21 , in accordance with an embodiment of the present invention. In the current embodiment, a digital camera  42 , such as an intensified charge coupled device (“CCD”) camera or digital camcorder equipped with a UV filter  44 , is used to take an image of a suspected area of evidence  32 . An initial background image  46  is taken of the suspected area of evidence  32  to indicate background levels of ambient UV reflected and fluorescent light. An evidence-exposing fluorescence image including the background image  46  or evidence-plus-background image  48  is taken immediately after the suspected area of evidence  32  is exposed to a flash UV light source  34 . The flash UV light source  34  generates a high-intensity pulse  36  of UV radiation  38 . The high-intensity pulse  36  of UV radiation  38  excites evidence  40  (evidence types  40   a ,  40   b ) such that evidence  40  fluoresces. 
     The flash UV system uses UV light to inspect areas that may be contaminated. The system operates by pulsing the light through a triggering device that also activates the shutter of a CCD camera, which takes a digital picture of the resultant fluorescence. In addition to the CCD camera, supporting software for the camera allows changes to the gain settings and sensitivity to the wavelengths of interest. The various embodiments of the present invention allow an investigator to photograph areas of interest without normal photographic film, which may or may not show the image that the investigator sees. The camera, through the use of notch filters, and software allow the investigator to use various wavelengths. 
     UV flash fluorescence is luminescence due to absorption of UV radiation by outer shell electrons followed by immediate re-radiation (fluorescence) in the form of visible light that ceases almost as soon as the incident UV radiation stops (atoms return to the ground state). The pulsed light gives a greater equivalent of power than the continuous UV source found in hand held backlights (approximately 50 kW compared to 100 W from a continuous source). 
     The initial background image  46  and the evidence-plus-background image  48  are transferred to a computer  50 . An image processing package  52  subtracts the initial background image  46  from the evidence-plus-background image  48 , resulting in a composite evidence or an evidence-only image  54 . The evidence-only image  54  is displayed on the computer display  56 . The evidence-only image  54  is also analyzed by an image analysis package  58 , resulting in analysis data  60 . 
     The components of the combined forensic evidence detection and analysis system  21 , i.e., the flash UV light source  34 , the digital camera  42  and the computer  50 , are interconnected such that the digital camera  42 , including lens  43 , will only take the evidence-plus-background image  48  immediately after a pulse of the flash UV light source  34 . This timing control  35  may be implemented via a direct connection between the flash UV light source  34  and the digital camera  42 , or, alternatively, it may be implemented via software control, meaning that both the flash UV light source  34  and the digital camera  42  are connected to the computer  50 . Additionally, transfer of image data between the digital camera  42  and computer  50  may be accomplished through a variety of methods. Image data may be stored by the digital camera  42  onto a storage medium  62 , which storage medium  62  may be transferred to an appropriate media-reading device  64  connected to the computer  50 . Image data may also be transferred directly from the digital camera  42  to the computer  50  via a hard-wired or wireless connection. By way of example and not limitation, an exemplary suitable camera may include a “Retiga 1300i” available from Q Imaging of Burnaby, B.C., Canada. 
     Other control systems include a range-finding system  68 , preferably utilizing a range-finding laser, connected to either the digital camera  42  or the flash UV light source  34 . The range-finding system  68  will only allow the forensic evidence detection and analysis system  21  to function when the digital camera  42  and the flash UV light source  34  are within an appropriate range of the suspected area of evidence  32 . 
     The flash UV light source  34  is implemented by use of a lamp that emits a high-intensity pulse  36  of radiation in the UV, visible and infra-red (“IR”) ranges. Specifically, the flash UV light source  34  emits radiation in the ranges of 140 nm to 1100 nm, and may emit either a wide-band pulse or a tunable narrow-band pulse at a specific wavelength. The high-intensity pulse  36  is of sufficient intensity to adequately illuminate a suspected area of evidence  32  that is many square feet in area, from a distance of several feet. Additionally, the high-intensity pulse  36  is of sufficient intensity to cause to fluoresce any fluorescent evidence  40  within the illuminated area of the suspected area evidence  32 . By way of example, the suspected area of evidence  32  may be on the order of multiple square inches to multiple square feet, depending on the range and resolution of the digital camera  42 . In one example, the focal length of the digital camera  42  is on the order of tens of inches. By way of example and not limitation, exemplary suitable UV light sources include a “Perkin-Elmer FX-249U” (Xenon lamp, 4 Joules/flash, 60 W power) or a “Perkin-Elmer FX-4400” (Xenon lamp w/parabolic reflector, 1 Joule/flash, 60 W power) both available from PerkinElmer Optoelectronics of Fremont, Calif. 
     By way of example and not limitation, most of the materials of forensic interest fluoresce at approximately 300 nm. The system through the changing of sources and the use of filters is capable of working with multiple wavelengths, and is not limited to any one wavelength. The present invention contemplates the use of multiple wavelength (300 nm, 350 nm, and 385 nm) sources, and firing, for example, them in sequence, with spectra for each excitation being collected. The composite spectrum could then be stored for each material in a library within the system. Through software signal processing of the spectra contamination type, the specific contamination type could be identified. 
     Specifically, the forensic evidence detection and analysis system  21  uses UV light to inspect the suspected area of evidence  32  that may be contaminated. According to the forensic evidence detection and analysis system  21 , the flash UV light source  34  is not continuously activated. The light is pulsed through timing control  35  that also activates the shutter of the digital camera  42 , which takes a digital image of the resultant fluorescence. In addition to the digital camera  42 , the supporting software for the digital camera  42  allows changes to the gain settings and sensitivity to the wavelengths of interest. In the present embodiment, the digital camera  42  relieves for example, the forensic investigator from the need to photograph areas of interest with conventional light-sensitive photographic film, which may or may not show the image that the investigator perceives. The digital camera  42 , through the use of filters  44  (e.g., one or more notch filters), and software allow, for example, the investigator to use a wavelength of choice; thus the technique is not limited, as are most black light systems, to any one fixed wavelength (e.g., 365 nm). By way of example and not limitation, exemplary suitable filters include: “Hoya U-340,” UV Bandpass filter, 1-inch dia, center 340 nm, half transmittance width 85 nm, available from Hoya Corp. of Tokyo, Japan; “Andover UG-11”, UV Bandpass filter, 1-inch dia, center 330 nm, half transmittance width 85 nm, available from Andover Corp. of Salem, N.H.; “Schott BG-38”, Low wavelength bandpass, 1-inch dia, center 480 nm, half transmittance width 380 nm, available from Schott, Inc. of Elmsford, N.Y. 
     In fact, wavelengths in the present system may be selected based upon the anticipated substances of interest. For example, most substances of forensic interest (e.g., blood, saliva, semen, etc.) fluoresce at a wavelength of approximately 300nm. According to the system of the present embodiment, multiple wavelengths of UV radiation  38  may be utilized in conjunction with corresponding filters  44  to enhance fluorescence of specific substances of particular interest. Furthermore, multiple wavelengths (e.g., 300 nm, 350 nm, and 385 nm) may be consecutively sequenced with the corresponding spectra collected from each excitation. Further analysis may be performed beyond the initial location of the substances. For example, the composite spectrum of each substance may be stored in a reference library within the system. Through, for example, signal processing of the spectra resulting from the evidence under analysis, a specific type of substance may be correlated with reference to the reference spectra of the reference library. 
     Generally, UV fluorescence, according to the various embodiments of the present invention using the forensic evidence detection and analysis system  21 , utilize luminescence due to absorption of UV radiation by outer shell electrons followed by immediate re-radiation (fluorescence) in the form of visible light that ceases almost as soon as the incident UV radiation stops (i.e., atoms return to the ground state). Employing the flash UV light source  34  provides a greater equivalent of power than is generally available through a continuous UV source (i.e., approximately 50 kW from a flash UV system compared to 100 W from a nonflash or continuous source). 
       FIG. 3  shows a forensic evidence detection system  22 , in accordance with an embodiment of the present invention, wherein the evidence  40  includes multiple evidence types  40   a  and  40   b . Evidence type  40   a  is excited at a specific wavelength contained in the spectrum of UV radiation  38  emitted by the flash UV light source  34 . Evidence type  40   a  will subsequently fluoresce at a different fluorescing wavelength  66   a . Evidence type  40   b  may similarly be excited at a specific wavelength contained in the spectrum of UV radiation  38  resulting in fluorescence at yet another fluorescing wavelength  66   b . Saliva, semen, sweat, etc., each fluoresce at a distinguishing wavelength, thus allowing the image analysis package  58  ( FIG. 1 ) to both distinguish and identify evidence types  40   a  and  40   b.    
     Fingerprints, for example, will fluoresce if exposed to a sufficiently intense pulse of UV radiation without the use of dusting powders due to the energy of the pulsed UV source. Since more energy is available from the pulsed UV source than from conventional, continuous or non-flash sources, more of the UV radiation is absorbed which causes the fingerprints to fluoresce. Furthermore, the flash UV system is unlike a black light system because the pulsed system, due to the higher UV energy, is capable of being used in normal ambient lighting conditions. In contrast, a black light system must be used in a room with an extremely low ambient light level. 
     Blood, on the other hand, does not naturally fluoresce, but instead absorbs UV radiation. An area of absorbed UV radiation is still detectable in the evidence-plus-background image  48  as an area absent of any reflected or fluoresced UV radiation. Detection of the multiple fluorescing wavelengths  66   a  and  66   b  requires a UV filter  44  to be attached to the digital camera  42 . The UV filter  44  may include multiple filters for specific fluorescing wavelengths  66   a  and  66   b  or a single tunable filter. The UV filter  44  will collectively pass UV wavelengths in the range of 330 nm to 450 nm. Additionally, the range-finding system  68  is shown connected to the digital camera  42 , assisting proper orientation and positioning of the digital camera  42  and flash UV light source  34  to within an acceptable range of the suspected area of evidence  32 . 
       FIG. 4  illustrates an exemplary display  23 , in accordance with an embodiment of the present invention. Computer display  56  shows the evidence-only image  54 , although other images, such as the initial background image  46  ( FIG. 1 ) and the evidence-plus-background image  48  ( FIG. 1 ) may also be viewed. The sampled resolution of the viewed images may be selected. Additionally, analysis data  60  collected from the image analysis package  58  ( FIG. 1 ) may also be displayed. In  FIG. 4 , two evidence types  40   a  and  40   b  are shown. For each evidence type  40   a ,  40   b , a fluorescing wavelength  66   a  and  66   b  and fluorescence intensity may be indicated. The size and location of the evidence types  40   a ,  40   b  are also indicated. Additionally, in another embodiment of the present invention, multiple evidence-plus-background images  48  ( FIG. 1 ) may be rapidly taken so as to allow calculation by the image analysis package  58  ( FIG. 1 ) of a fluorescence time constant for each evidence type  40   a ,  40   b , indicating the attenuation rate of each fluorescing wavelength  66   a ,  66   b.    
     The foregoing detailed description of the present invention is provided for purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Accordingly, the scope of the present invention is defined by the following claims.