In the early 80's while performing autopsies on the victims pathologists and medical technicians recovered small amounts of DNA left by the killer. Those samples, principally semen, were retained as evidence.
Investigators had previously tried DNA analysis using older techniques but didn't have enough material.
When King County Sheriff's searched Gary Ridgway's home, in 1987, they had him chew a piece of gauze. This saliva sample would end up providing evidence for future DNA tests. March 2001, advances in DNA typing technology identified the source of the semen. September 4, 2001, the lab received results on the first sample. Johnston said the lab was able to get a comparative match from evidence gathered at the crime scenes and Ridgway's saliva.
Sperm samples taken from Carol Christensen matched Ridgway's DNA. Not more than one individual in the world, excluding identical twins, would exhibit this DNA profile. Ridgway's DNA profile was likely present in Opal Mills, 16 and Marcia Chapman, 31. DNA findings from Chapman's sample indicated a partial profile consistent with Ridgway's. Mills indicated a mixed profile and Ridgway's could not be eliminated as source. The "analytical part," takes about a day. After the first match, work on the case stepped up. 3 scientists qualified to do STR worked more than 640 hours.
"A physical examination doesn't tell you if you have enough DNA there to test," said Barry Logan, director of the Washington State Patrol's Forensic Laboratory Services Bureau. "You have to do the test to know. In theory, a cell is enough."
DNA typing became available in the early 1990s but required large samples. Two or three years ago, finding a match to the DNA in his saliva required a sample the size of a quarter sized stain to narrow a suspect down to one in 20,000 people.
In 1987, "DNA wasn't on anybody's mind at all." The sample was taken for blood type analysis, said King County sheriff's spokesman, John Urquhart.
In the beginning of the investigation, forensic scientists could only compare blood types and crude evidence. Blood analysis typing blood or saliva as A, B, O was an early method of matching samples taken from suspects and evidence at crime scenes. It was routinely performed in sex crimes. Blood typing eliminates suspects, but it cannot tie a suspect to a crime as DNA does. Detectives had to wait for DNA technology to process old, unpreserved and microscopic bits of substance that could yield an accurate DNA reading.
Kary Mullis, chemist at the University of California, Berkeley, came up with the concept of PCR in the mid-1980s, it took years for the technique to be perfected and reliable enough to be accepted in forensics and eventually won the Nobel Prize.
The policy at the King County Medical Examiner's Office is to ambitiously collect and preserve evidence. Dr. Richard Harruff, chief medical examiner says, "The concept is that we don't know what happened, we don't know what the circumstances are, and we only have one chance to do the right thing, so we do everything we can. We don't regard anything as too deteriorated to collect."
Forensic scientists must analyze and reanalyze 10,000 pieces of related evidence, including bird nests, pieces of paper, clothing, pop cans, cigarettes, fibers, hairs and soil, stored away for almost 20 years. That doesn't include items recently taken from Ridgway's homes and vehicles. With STR typing, those boxes of watches and jewelry could be a gold mine.
Most Green River evidence is still being looked at for suitability for STR typing, identifying the ones with the best chance of yielding DNA. Evidence already tested will be retested, because a DNA profile obtained with the older techniques can't be compared with one obtained with STR. Investigators hoped items would provide new links to additional victims. Each piece of evidence was handled by an STR-trained forensic scientist.
They begin the search with a visible stain under a bright light. A chemical agent will reveal semen stains. After the DNA is found, it is evaluated, quantified, copied and analyzed with a $55,000 capillary electrophoresis machine, a report and peer review. This took about a month.
The Medical Examiners' Office dried blood samples instead of freezing them. They kept better and were easier to store. In addition to lifting fingerprints from the neck of a strangulation victim, they swab for skin cells.
Copyright Kari Sable 1994-2011