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By Nathan Welton
The Tribune
June 3, 2004


Microscopic strands of DNA, perhaps collected from a pinhead-sized drop of blood, led deputies to a suspect this week in an 18-year-old murder case.

Arroyo Grande landscaper Peter Derks, 57, was taken into custody Tuesday on suspicion of the 1985 murder of former Cal Poly student Mary Catherine Waterbury. She had been sexually assaulted and strangled in Montana de Oro State Park.

"This is significant because it's the first time we've made a murder case in San Luis Obispo County based on a DNA match," said county Sheriff-Coroner Pat Hedges.

Waterbury's slaying had remained unsolved for almost 20 years, but new DNA analysis helped justify the arrest, deputies said Wednesday. Investigators also said the department has at least two other unsolved cases to which they're applying the technology.

Along with two dozen others, Derks had been considered in the case over the years, but deputies never had enough conclusive evidence to take action.

Waterbury's family could not be reached for comment Wednesday. Hedges said the recent developments had upset them.

Still, "they were pleased there was potential closure in the case," said Sheriff's Detective Jay Donovan, who contacted the family Tuesday.


On Oct. 19, 1985, the 23-year-old Waterbury left her San Luis Obispo apartment to watch the sun set at Montana de Oro State Park.

She was never seen again.

She had been taking time off from Cal Poly to work as a bookkeeper for the San Luis Record Co. but enjoyed spending her free time in the park.

Her brother, Chris, became worried when she didn't come home to the apartment she shared with her sister, Julie. He knew she liked the park and went there to look for her the next day.

He found the car she'd driven, her sister's yellow Volkswagen, abandoned inside the park off Pecho Valley Road. He then called San Luis Obispo police, who called search-and-rescue teams.

A storm that night hampered efforts, and officials believed the waters washed away potentially useful evidence. The rain was so torrential it rendered bloodhounds ineffectual.

Two days after Waterbury disappeared -- and after 100 soggy searchers turned up nothing -- a helicopter search party spotted the woman's body.

Waterbury's partially clothed, unhidden body was laying in thick brush 300 yards from the car. Crime scene investigators took samples of hair, blood and bodily fluid.

An autopsy later revealed she had been sexually assaulted and strangled.

On the trail

At the time, limited forensics technology allowed officials to make only crude biological comparisons, such as basic blood matching, with the evidence.

"What we could use it for back then was much more primitive than what we could use it for now," Hedges said. "But we collected evidence, we preserved evidence, and sometimes science works in your favor."

Officials saved the samples and continued the investigation. Over the years, leads trickled in, but the case remained stalled.

In 1990, deputies submitted their crime scene samples for genetic testing. It was then they discovered the evidence had identifiable DNA -- both of Waterbury and of an unknown other person.

The suspect

Meanwhile, about two years after the Waterbury murder, Derks was convicted for assaulting a woman with a deadly weapon.

The crime occurred in the same park deputies say he killed Waterbury.

Derks emerged from prison in 1991. State law enforcement officials took a DNA sample from him before he left, Hedges said, and added it to a government database of known criminals for later comparison.

Hedges also said that Derks had a conviction in Texas in the early 1970s that, had it occurred here, would have mandated his registration as a sex offender.

A new lead

Through the 1990s, no matches returned from Sacramento, and the state's DNA storage bank remained relatively unused for the next decade, said Nathan Barankin, spokesman for the state Attorney General's office.

But Attorney General Bill Lockyer took office in 1999 and placed new focus on emerging DNA technologies, processing a 140,000-sample backlog, Barankin said.

Upon learning of the new emphasis on DNA testing from Lockyer's office, Hedges said, local authorities resubmitted crime scene evidence last year.

On May 14, local officials learned of a match between their submission and Derks' DNA.

His genetic profile is now one of an estimated 210,000 on file.

"We now have thousands of samples in the database," said Department of Justice Special Agent Steve Utter.

Now, Hedges said, authorities are considering Derks for other unsolved crimes in the county. They include the suspected 1998 murder of Andrea Hug, whose body investigators also found in Montana de Oro State Park.

Arrest in Arroyo Grande

Officials apprehended Derks on Tuesday following a two-week surveillance of his Tally Ho Road home.
Derks' neighbor Ron Kautz said the man was a quiet type who rents an apartment above the main house, kept up the lawn and did other odd jobs. He lived there for at least five or six years, the neighbor said.

"He comes and goes quietly," Kautz said. "He was not a nuisance."

Authorities spent a lot of time searching his yard and garage Tuesday, said Kautz, who lives across the street. Kautz said state agents questioned him after showing him a picture of an unkempt man to identify. He had never seen Derks up close and wasn't sure he was his neighbor.

"He was always much better groomed when I saw him," Kautz said. "I told them, 'I guess it could be the man across the street.'

"I didn't know him by name but I always said 'Good morning' when I'd go out to get the mail. He nodded, but that was about it."