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.
had previously tried DNA analysis using older techniques but
didn't have enough material.
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
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.
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.
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."
typing became available in the early 1990s but required large
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.
"DNA wasn't on anybody's mind at all." The sample was taken
for blood type analysis, said King County sheriff's spokesman,
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
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.
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."
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.
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
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.
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.