Lab analysis more accurate than ever

MAT-SU -- The first time Alaska's state crime lab took DNA fingerprinting evidence into court it was during a Fairbanks murder case in 1992, according to crime lab director Chris Beheim. The DNA evidence was accurate 11 years ago, but not nearly as accurate as it is today.

In the 1992 case, the crime lab used DNA analysis to help investigators eliminate one suspect. Weeks later they used the technique to show that traces of blood found inside a watchband seized from a second suspect was originally from the victim. The techniques of the time showed that the odds of the blood being from anyone except the Fairbanks victim was something on the order of one in 10,000, according to Beheim.

"You could eliminate 99 percent of the people," Behiem said. "It wasn't as astronomical as it is now."

Stretched out, each double-helix molecule that is coiled inside every cell in your body would be about five feet long. Scientists can look at parts of the molecule that we all have in common and at the parts in-between to find subtle differences. In the United States, forensic investigators use a standardized 13-marker technique, examining 13 parts of the molecule to describe the person.

Identical twins are an exception, but aside from that, the odds against two different people having identical matching DNA fingerprints using today's technology could be as high as one in 2.11 quintillion.

Imagine the 13 markers as if there are rolling digits in the combination lock on a suitcase. The 13 markers can be located in every human DNA molecule, but like the tumblers on a lock they can be set differently. And all of 13 are not as simple as a 10-digit tumbler.

"One might be found in one in five people and another might be found in one in 12 people," Beheim said.

Two suspects might have one or more markers in common, but when you compound the odds of all 13 markers coming up identical you get 2.11 quintillion to one.

"It's usually less than that, but still, it's still many, many times the world's population," Beheim said.