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.
The saliva sample ended 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.
Since
the results came back 2 months ago investigators have tried
to link him to more cases. Investigators had approximately 8,000
pieces of evidence to work through.
The
DNA linking Gary Ridgway to
3 of the for 4 women he is
charged with killing is conclusive in one case but less certain
in two others.
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.
An affidavit
authorities used to jail Ridgway indicates tests performed by
the Washington State crime lab found that 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.
A great
deal of time was spent obtaining a good sample from degraded
material. 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. 2
or 3 years ago, finding a match to the DNA in his saliva would
require a sample the size of a quarter sized stain to narrow
a suspect down to only one in about 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 and former Deputy Prosecutor Al Matthews.
In the
beginning of the investigation, forensic scientists could only
compare blood types and other 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 can eliminate
suspects, it cannot tie a suspect to a crime as DNA does.
Detectives
had to wait for DNA technology to be able 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 prove reliable enough to be
accepted in forensics. He eventually won the Nobel Prize.
The
policy at the King County Medical Examiner's Office is to ambitiously
collect and preserve evidence, says Dr. Richard Harruff, chief
medical examiner. "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
hope items may provide new links to additional victims. Each
piece of evidence will be handled by an STR-trained forensic
scientist.
They
begin the search with a visible stain under a bright light.
A chemical agent and several steps will reveal semen stains
in glowing pink. After the DNA is found, it is evaluated, quantified,
copied and analyzed with a $55,000 capillary electrophoresis
machine, then a report and peer review. This takes about a month.
The
Medical Examiners' Office dries blood samples now instead of
freezing them. They keep better and are easier to store. Now,
in addition to lifting fingerprints from the neck of a strangulation
victim, they swab for skin cells.
Kari
& Associates
PO Box 7372
Olympia, WA 98507
Copyright Kari Sable Burns 1994-2006
