A new kind of DNA technology gives police a more powerful tool to identify suspects.
By Eric Adler, The Kansas City Star
Time was when a tossed cigarette butt, lost ball cap or crushed beer can were all but useless to a crime lab.
Maybe, if investigators were lucky, they could swab them and find an odd protein or blood group that might help narrow their list of possible suspects. If, that is, they didn’t already have a good fingerprint.
Since the late 1990s, however, a kind of DNA science that Kansas City police crime lab director Gary Howell calls “powerful, powerful technology” has changed all that.
“Now the cigarette butt is important, the beer can is important, the sweat on the ball cap is important. Now we can potentially identify suspects,” Howell said Monday. “And that is on rape cases, homicide cases, burglaries. We have identified DNA from the sweat out of gloves.”
It’s a technology that wasn’t perfected in the days of O.J. Simpson. Today the technique, called PCR/STR (polymerase chain reaction/standard tandem repeats) has brought the odds of identifying suspects from one in 20 in the old blood grouping days to one in 18 quadrillion.
Of course, like all sciences, DNA “fingerprinting” has evolved.
In the late 1980s and early 1990s, crime investigators used a DNA technology called RFLP — for restriction fragment length polymorphism. With this technique, scientists used radioactive “probes” to hook on to pieces of DNA. Just like an individual’s DNA, the pattern of radioactive decay is unique. The technology was extremely accurate in identifying suspects but cumbersome.
Also, the tests took weeks. If the DNA (the deoxyribonucleic acid molecule that is unique to all living creatures) wasn’t present in enough quantity, or if it was old or damaged, a good test couldn’t be done.
PCR, meantime, is easier, less expensive and more reliable. It also does not require lots of DNA.
That’s because scientists can make as many copies as they want of whatever DNA they find. This gives them an unlimited supply to do unlimited tests. From a tiny speck of DNA from 50 years back, scientists can use the new technology to make a fresh copy.
Then they analyze it, mapping specific spots on as many as 13 chromosomes. The chances that these spots on the 13 chromosomes will be the same in any two people (other than clones or identical twins) are one in 18 quadrillion.
How long does such a test take? As little as two days.
That DNA information is then fed into an FBI DNA database, which keeps information on tens of thousands of convicted felons .
But with the Kansas City police crime lab’s six DNA scientists doing work for 106 regional law enforcement agencies, finding those suspects can also take time.
“We have hundreds and hundreds of samples from current cases let alone the thousands on cold cases,” Howell said. “Everybody thinks we can do it in two days. It doesn’t work like that.”