Mary Catherine Waterbury: Killed in Montana de Oro in 1985

April 14, 2010 

On Oct. 19, 1985, Cal Poly student Mary Catherine Waterbury was watching the sunset at Montana de Oro. Someone then raped her before stuffing her face in the sand until she suffocated.

Twenty years later, Peter Derks was sentenced to life in prison without the possibility of parole for the crime.

The 2004 arrest of a Derks was based on a DNA match in the state database. It was the first time in San Luis Obispo County that investigators made an arrest in a murder case based on a DNA match in the state database.

Derks, who had a 1973 rape conviction in Texas, was considered a suspect at the time of the murder, but deputies did not have enough evidence to make an arrest.

In 1987, he pleaded guilty to threatening a 20-year-old woman with a wooden club along a trail in Montana de Oro. After serving four years in state prison, a DNA sample was taken from him. Investigators later matched his DNA to semen found on Waterbury.

Derks pleaded guilty to felony charges of premeditated murder, forcible oral copulation and rape by force. The plea bargain allowed him to avoid the death penalty.

The Waterbury family declined to speak during and after Derks' sentencing but provided a statement to the media calling the hearing "the conclusion of a 20-year journey of hope and faith."

They also thanked the Sheriff's Department, the District Attorney's Office and others for working on the case.

"Mary's brief life was an incredible gift to all who knew her; she will always be a presence in our lives," said the statement.

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