Sonoma County District Attorney Jill Ravitch said emerging reports that patients of the Sonoma Developmental Center have suffered chronic abuse at the hands of staff is a major concern and should be addressed by local authorities.

"I'm very concerned at the oversight at the developmental center," Ravitch said. "You've got a vulnerable population and there is an allegation that harm has been brought upon individuals there -- of course I have a concern."

But while the Eldridge center that houses developmentally disabled adults is within the boundaries of the Sonoma County Sheriff's Office jurisdiction, the institution is a state facility with its own police force that handles most investigations.

"We are not part of that process until they say they want the Sheriff's Office to investigate," Sonoma County Assistant Sheriff Lorenzo Due?s said.

The Sheriff's Office has an agreement with the Office of Protective Services, which polices state facilities, that it will handle criminal cases at the Eldridge facility upon request.

This fall, center police asked sheriff's detectives to take over their investigation into a caregiver accused of using a stun gun on 11 severely disabled patients.

An anonymous tip led state police to look into the staffer. And while doctors reported physical evidence of stun-gun injuries on patients and officers found a Taser in the staffer's car, the investigation apparently languished.

The Sheriff's Office was asked to take over nearly a year later.

Last spring, the center asked detectives with the sheriff's sexual assault team to investigate a report that a longtime employee forced a patient with the mental capacity of a 4-year-old to fondle his penis.

Another employee saw the incident.

Rue Le Roy Denoncourt, 53, of Sonoma was sentenced in August to eight months in jail and classified as a sex offender after he admitted to the May 25 assault as well as trying a similar act two weeks earlier with the patient's roommate.

"When they ask for our help, we'll take it over," Due?s said.

That will change with Gov. Jerry Brown's signing of a bill from state Sen. Mark Leno, D-San Francisco, that will require state facilities to immediately report sexual assaults, assaults with a deadly weapon and deaths to local law enforcement agencies.

That change will be welcome, Ravitch said.

"Local law enforcement are better equipped to deal with those types of investigations," Ravitch said. "They have all the training and professionals on staff."

You can reach Staff Writer Julie Johnson at 521-5220, or on Twitter @jjpressdem.