Forensic Friday: Who's Got the Goods?

Colonel Mustard did it with a knife in the library. Mrs. Peacock did it in the ballroom with a candlestick. But what if the evidence is contaminated, and the deed cannot be proven? That’s where chain of evidence comes in.

Chain of evidence, also called chain of custody, is the “chronological documentation showing the seizure, custody, control, transfer, analysis, and disposition of physical or electronic evidence.” The key to this process is for the chain to remain unbroken.

In order for evidence to be used in court to convict someone of a crime, it must be handled in a manner that prevents tampering. The handling must establish that the alleged evidence is in fact related to the alleged crime, rather than having, for example, been “planted” to make someone appear guilty. If there are discrepancies in the process, and it cannot be proven who had the item at a particular point in time, then the chain of custody is severed, and the defendant can ask to have the resulting evidence declared inadmissible.

An identifiable person must always have the physical custody of a piece of evidence, and each transaction involving the evidence must be recorded. Typically, a police officer or detective takes charge of a piece of evidence collected at the crime scene and gives it to an evidence clerk for storage in a secure place.

For those of you who watch CSI or any of the other police dramas on television, you may already be familiar with the process of evidence collection. Documentation begins at the crime scene where a technician photographs the item in its place. Then measurements are taken to indicate the exact location of the item at the scene. A common method to do this is for the technician to select a fixed point at the scene (e.g., the south side of the living room) then measure the distance to the evidence from that point.

Television often portrays police work as fast-paced, glamorous, and exciting. I’m sure it can be, but more often than not a criminal has been convicted because of a tiny anomaly brought to light by meticulous attention to some detail related to the case. (Think Sherlock Holmes or Monk.)

Who is your favorite TV detective?

 

 

 

Forensic Friday: What do Mining, Fireflies and CSI have in Common?

Crime scene investigation is predicated on the theory that no crime can be committed without leaving some sort of evidence behind. Even the tiniest trace. That’s where the chemical Luminol comes in. When mixed with an appropriate oxidizing agent, Luminol exhibits a soft, blue glow. This reaction is known as chemiluminescence, and it’s the same phenomenon that makes fireflies glow.

In crime solving situations, the oxidizing agent is the iron found in

hemoglobin (blood). During testing, the room is darkened, and the CSI technician sprays the chemical evenly across the suspected area. If blood is present, whether fresh or dried, the area will glow for about thirty seconds, and the effect can be documented by a long-exposure photograph. The intensity of the glow does not indicate the original amount present, but indicates only the distribution of trace amounts of substance left behind. Most people don’t realize that tiny particles of blood will cling to most surfaces for years.

Other substances do cause Luminol to glow, so additional tests are required for verification of the results. And because the chemical reaction can destroy other evidence, Luminol may be used only after pursuing other investigative options. It is not used as readily as shown on many television programs.

I was surprised to discover the chemical was originally designed in the 1920s for the German copper mining industry to reveal new sources of ore. It was not until 1937 that German forensic scientist Walter Specht made extensive studies of applying Luminol to crime scenes. Further study was done in 1939 in San Francisco that helped convince law enforcement officers of Luminol’s importance as a crime solving tool.

What other industries have contributed to crime solving?

CSI: The Early Years

As part of my blog re-launch, I'll be running some of my past posts. Here is one of the more popular ones:

More than 2,000 years before William Peterson or Marg Helgenberger prowled Las Vegas to collect evidence and solve crimes, the attending physician for Julius Caesar stated that of the 23 wounds on his body, only one was fatal. Fast forward to 1247 when the first textbook of forensic medicine was published in China. Nearly 400 years later the first book on document examination was published in France. The wheels of progress ground slowly until 1829 when Scotland Yard was established - a mere six years later the Yard used the first bullet comparison to catch a murderer.

After that the discoveries came fast and furiously. Here are just a few:

• 1836 – James Marsh develops a test for arsenic in tissues
• 1853 – First test for hemoglobin
• 1863 – First published paper on time-since-death determinations using temperature
• 1883 – Alphonse Bertillon invents anthropometry to identify and differentiate criminals
• 1891 – First book published describing the use of physical evidence to solve crimes
• 1892 – Francis Galton classifies fingerprints into the basic patterns that are still used today

Enter the computer. Thanks to technology, information can now be collected in

databases and shared across borders. One such database is IAFIS - the Integrated Automated Fingerprint Identification System – the national fingerprint and criminal history system. It is the largest biometric database in the world, housing the fingerprints and criminal histories for more than 70 million subjects in the criminal master file, along with more than 34 million civil prints. According to fbi.gov the average response time for IAFIS is 27 minutes. Compare that to the weeks or months spent combing over paper records in the past and consider that in 2010 IAFIS processed over 61 million submissions!

But wait! There's more. About twenty five years ago, the use of DNA matching became an integral part of solving crimes, and in 1995 the world's first national DNA database was set up in the UK. The US followed a short time later, and thanks to this wonder of science criminals have been caught, cold cases have been solved and innocent people have been released from prison.

I'll never look at those sticky fingerprints on the kitchen counter the same way again! How about you?