Crime Scene Investigator Network

Crime Scene Investigator Network Newsletter

APRIL 2018
This month's newsletter is brought to you by the 2018 CSI Summer Academy

Crime Scenes and
Alternate Light Sources

Don Penven

Alternate light sources, a much needed tool for CSIs

Over many decades, visible light sources were used during most searches of crime scenes. Although some forensic investigators would occasionally use ultraviolet (UV Black Light) to examine for crime scene evidence, white light was the mainstay. But in the 1970s the Royal Canadian Mounted Police (RCMP) added a new dimension to forensic examination of physical evidence.

The "Mounties" pioneered the use of argon-ion lasers, but these expensive, cumbersome, bulky machines were impractical for use at crime scenes, so their use was limited to the crime lab.

The birth of alternate light sources

Portable lasers began to appear in the marketplace in the 1980s, but their usefulness was limited to mostly a single color of light. In the 1990s the availability of high intensity incandescent lamps slowly revolutionized alternate light source analysis of physical evidence since these machines, many weighing less than 20 pounds, could provide an intense light beam that could be passed through various filters covering from visible blue, green, yellow and red light. Using these colors enhanced the ability to reveal an abundance of what would otherwise be invisible evidence. But one element is still missing.

What is fluorescence?

Merely shining a blue or other visible color light onto an object in and of itself does not show us much. You see, certain materials possess a property called fluorescence. Fluorescence occurs when light of a certain color and light frequency strikes an object, and the object returns light of a different color and frequency. This fluorescence is much weaker in intensity than the light beam that created it, so to visualize the fluorescence, the crime scene technician must use filtration that blocks the visible light but passes the fluorescence. For example: if the visible light beam is blue light, the filter must be orange in color. This blocks the intense blue light but passes the weak fluorescence. UV light, on the other hand, is invisible, but it produces visible fluorescence from certain objects and substances. No filtration is required to view UV fluorescence, but eye protection in the form of clear glass or plastic lenses is recommended.

Detecting hidden blood stains in crime scenes

If you watch many of the TV "Cop" shows, you will see at some point those working a crime scene using a blue light in search of invisible blood (blood stains that were cleaned up). Shazam! Blue-white stains appear all over the floors, walls and objects sitting around the crime scene! But in reality—this cannot happen. You see, blood does not fluoresce by applying UV or visible blue light.

Blood, even minute quantities that remain after clean-up, can be made to "luminesce;" that is, by spraying certain chemicals such as Luminol, BlueStar or Fluorescene on the various surfaces, blood will luminesce, or simply "glow in the dark"—and adding blue light is not necessary. So what can alternate light sources reveal? Although blood does not fluoresce, certain other physiological fluids will. UV alternate light sources can reveal the following: seminal fluid, saliva and urine stains. Also, certain narcotics will fluoresce as will bone and teeth fragments.

Other uses of alternate light sources Indeed, many forms of physical evidence will fluoresce. But modern science has resulted in the development of chemicals that "make" objects fluoresce. When using fluorescent chemicals, latent fingerprint development can be greatly improved. Fluorescent latent print powders have the ability to make the latent residue on a surface fluoresce. The benefit here is that the ridges fluoresce brightly and when photographed, a multi-colored or confused background can be minimized to the point where it does not show up in photographs. Fluorescent liquids are used to develop latent prints on porous surfaces such as paper and cardboard.

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This Month's Featured Resource on the Crime Scene Investigator Network Website

It is the intention of this Guide to acquaint a broad spectrum of public safety personnel with the fire investigation process, so they may understand their role in this important task and help identify, locate, and preserve evidence in its varied forms, to either assist a specialist investigator when one is needed or to adequately document and collect evidence when no assistance is needed or available. This Guide focuses on the documentation and collection of physical evidence at fire/arson scenes.

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New CSI and Forensic Job Announcements

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Crime Scene Evidence Technician II, USA
Final Filing Date: May 8, 2018
Responsible for the collection and preservation of evidence in criminal investigations and performing identification services to the public. Also responsible for responding to crime scenes for processing of evidence related to crimes.
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Crime Scene Specialist
Round Rock Police Department, Round Rock, Texas, USA

Final Filing Date: June 3, 2018
The Crime Scene Specialist responds to crime scenes and other serious incidents for the purpose of documenting and gathering evidence.
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Forensics Technician
Osceola County Sheriff's Office, Kissimmee, Florida, USA

Final Filing Date: Open until filled
The Forensic Technician performs technical work in criminal identification matters to include photography, collection and preservation of evidence, processing for latent fingerprints, examining biological substances, and physical documentation of crime scenes.
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Los Angeles Police Department, Los Angeles, California, USA

Final Filing Date: Continuous
A Criminalist searches for, collects and preserves physical evidence in the investigation of crime and suspected criminals; examines evidence by means of physical and chemical analyses; prepares reports of findings; and gives expert testimony in court. At the highest pay grade, performs analyses of physical and chemical evidence of a nonroutine nature requiring advanced technology; and may serve as a lead worker by providing training and supervision to criminalists working in a specialized field.
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Forensic Crime Laboratory Intern
South Bend Police Department, South Bend, Indiana, USA

Final Filing Date: Open until filled
This internship will consist of processing a variety of evidence including vehicles, DNA, fingerprints, and various items collected from crime scenes.
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Latent Print Examiner
Chula Vista Police Department, Chula Vista, California, USA

Final Filing Date: May 7, 2018
To perform a variety of complex tasks in the identification, classification, automation and comparison of latent prints in connection with the investigation of crimes; prepare presentation of evidence for court and serve as an expert on all phases of latent print identification; and to perform other related duties as assigned.
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