Four years ago, DNA evidence collected from the 1982 homicides of Mildred Wallace and Margie Call was tested to see if police could shed any light on the cases that had remained a mystery for more than two decades.

To the disappointment and frustration of police and family members of the victims, the tests, which compared the evidence taken from semen samples to three suspects, did not contain enough genetic material to secure a definite match.

Until now.

In October, evidence collected from the Wallace case was retested for comparison to Timothy W. Krajcir, a known rapist serving time in an Illinois prison on a sex offender statute.

This time, they found a match.

Kracjir was charged with the rape and murder of Call and Wallace, the 1977 murders of Brenda and Mary Parsh and Sheila Cole, and another rape from 1982, Cape Girardeau County Prosecuting Attorney Morley Swingle announced Monday at a news conference.

Kracjir has confessed to three unsolved murders in other states.

Because so little of the evidence remained, during the most recent round of tests, crime lab analysts relied on a method called polymerase chain reaction, or PCR, Swingle said.

"What has changed is from the time DNA testing started is that before, it took so much of it to match a suspect," Swingle said.

Recently, the case of Arthur Ivy, arrested Oct. 8 and charged with drug trafficking, brought the value of PCR to the forefront, Swingle said.

After a Cape Girardeau judge dismissed the charges against Ivy because he ruled there was no probable cause in the case, Swingle received a lab report from the state crime lab showing that Ivy had handled a baggie containing crack cocaine.

PCR allowed DNA testing to show a one in 1.6 quadrillion degree of accuracy, according to the lab report, despite no blood or other bodily fluid being on the bag.

Charges were refiled, and this time Ivy was bound over for circuit court.

The method, credited to Kary B. Mullis, who won the Nobel Prize for chemistry in 1993 for his work with PCR, works by amplifying tiny quantities of DNA by making millions of exact copies, according to Brian Hoey, a scientist with the Missouri State Highway Patrol Crime Laboratory.

Although the state crime lab had PCR technology in 2003, analysts might have considered the wrong piece of evidence when they did the first round of testing, Hoey said.

Mimics natural process

The principles that enable PCR had been known for years before Mullis perfected the method, because it mirrors what occurs naturally in the human body, he said. PCR is largely the same mechanism as mitosis, the process of cell duplication, but performed in a controlled laboratory environment instead of inside the body.

Once they have a sufficient quantity for analysis, scientists begin narrowing the field by comparing 16 core sequences of repeated DNA to see how many match.

He compared the process to that of police identifying a suspect in an armed robbery. If police knew they were looking for a suspect with black hair, that would eliminate some people, but it couldn't pinpoint one specific person, he said.

Adding height and eye color would narrow the group of suspects further but still wouldn't be enough to make an arrest.

What scientists do with DNA is try to match as many of the 16 sequences as possible to come up with a genetic description that could only fit one individual, he said.

When all 16 sequences are identified, that produces a one in 1.6 quadrillion match.

How many sequences they find determine what statistics they use.

The DNA found in the Wallace case produced a one in 720,000 match, Swingle said.

It's not unusual for DNA evidence in a case to be resubmitted after a test has been unsuccessful, like in the Wallace case, Hoey said.

"Sometimes you just need a new eyeball," he said.

Hoey said his lab receives about 500 cases per year requesting DNA comparisons.

bdicosmo@semissourian.com

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