21st-Century Crime Solving with DNA

By Collins, Elizabeth M. | Soldiers Magazine, June 2010 | Go to article overview

21st-Century Crime Solving with DNA


Collins, Elizabeth M., Soldiers Magazine


DNA--three small letters that have drastically changed the world and forever altered how crimes are investigated and prosecuted.

More formally known as deoxyribonucleic acid, DNA contains the genetic makeup of every living organism and is unique to each individual, except in the case of identical twins. DNA collected from a crime scene can be compared against a suspect's to prove whether or not he was present at the scene.

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The DNA Branch at the U.S. Army Criminal Investigation Laboratory, Fort Gillem, Ga., which serves all branches of the Department of Defense, has recently doubled in size. About 50 examiners at the lab process around 90-95 cases a month, mostly looking at blood, semen and saliva, although they also have the capability to examine tissue, urine and hair.

In the past two decades, DNA techniques have become so sensitive and advanced that examiners can often obtain usable DNA samples by testing places a suspect or victim merely touched. If a suspect grabs a victim's lapels, for example, examiners may be able to obtain DNA from those lapels.

In addition, chief DNA examiner Jeffrey "Fletch" Fletcher can lift DNA from the underarms or collar of a seemingly unstained shirt, and has been able to identify, or clear, alleged sex offenders based on touch DNA on victims' bra cups. He has also found the DNA of victims on the inside of suspects' underwear.

"You'd be amazed what we can get DNA from," said Fletcher. In fact, the DNA replication, extraction and comparison process has become so streamlined that a sample as small as a pencil point can be processed in a matter of days. The hardest part is finding the DNA to test.

"When we're talking about doing a sexual assault examination--and let's say it has multiple suspects, and let's say the bedding has not been laundered in quite some time ... you're looking at maybe a comforter or a sheet that has 80-plus stains, and ... you have to almost test them all," Fletcher explained, adding that when he worked for a state crime lab, he couldn't spend weeks pouring over evidence the way he does at USACIL.

"What I like about CID and the military is, 'do what has to be done.' If it takes a little longer to get a case done, we want to get it done the first time. We're a little more thorough in our analysis in the sense that we would examine evidence that maybe in a state lab wouldn't be probative. From this aspect, we're able to look at everything," he continued.

In order for a DNA sample to do investigators and prosecutors any good, however, it must be compared against a "known standard," in other words, a sample taken from a suspect or victim. Once the two samples have been processed, a computer printout lists the number of times each particular code repeats itself, and the examiner compares the two.

Although 99.7 percent of DNA A is the same for everyone, according to Fletcher, certain regions on the DNA strand vary greatly. Examiners look at about 15 of those regions, and can say with certainty if two DNA samples came from the same person, and add a statistical weight. Fletcher said this is where experts come up with numbers like a one-in-50-billion chance of the sample occurring naturally in a different person. Since there are far less than 50 billion people on earth, it's an identity statement. All it says, however, is that a suspect was at a crime scene or came in contact with a victim, it doesn't say why or how. …

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