An 81-year-old retired psychologist who advocated for patients with Parkinson's disease was found stabbed to death in his home in the small East Bay community of Kensington, authorities said Tuesday, and a woman described as his friend and regular companion was arrested.

James Durkin's body was found Monday at his home on the 600 block of Coventry Road, a hillside dwelling with views of the bay. A caretaker found Durkin, a knife still sticking out of his chest, authorities said.

Early Tuesday, police arrested Diane Sydenham, 56, at her Albany home. Acquaintances said she was Durkin's companion.

Harold Jewett, a Contra Costa County deputy district attorney, declined to discuss a possible motive for the slaying but said the two had been friends. Neighbors said Sydenham had never lived in Durkin's five-bedroom home, which is divided into several in-law units, but had been a frequent visitor.

Sydenham was being held on suspicion of murder at Contra Costa County Jail in Martinez. Bail was set at $1 million.

'Very emotional'

From her jail cell Tuesday, Sydenham declined an interview request, saying she needed to consult with her attorney.

Her lawyer, Robert Beles, said Sydenham has no criminal history. "She's very emotional and distraught," said Beles, who declined to comment further.

The slaying sent ripples of shock through Kensington, an exclusive enclave of 5,000 where violence is rare.

A caretaker for a woman who lives in a separate part of Durkin's home said she had found the body.

Durkin and Sydenham often argued, said the caretaker, who asked not to be identified by name because the police investigation was continuing.

Although some neighbors said they didn't know Durkin had been involved romantically, the caretaker said the two did have such a relationship - but that it had been rocky at times.

"They were fighting," she said.

The woman said Durkin was "a great guy. He was a psychologist, he was a writer, he wrote poems. He was just a loving guy."

Diagnosed with Parkinson's

Durkin's ex-wife, who did not want to be identified, said he had been diagnosed with Parkinson's disease about eight years ago and had been helping other patients with the illness.

She said she spoke by phone with Durkin about two weeks ago. "I was quite amazed. He sounded quite good," she said.

"Jim was an extremely bright, creative individual, just really engaging," she said. "People really liked him."

Durkin leaves behind his daughter, Carla Durkin, a marriage and family therapist in San Francisco, and son, Larry Durkin, who works in medical market research in Pennsylvania.

Helping patients

"He believed patients could have a voice, and in the process of finding new treatments, he felt he could do a better job of organizing people's thinking and their stories in a way that would yield much more useful data to the clinical researchers," Larry Durkin said.

His wife, Connie Lee, agreed, saying, "Until the last day, I think he was doing research on Parkinson's. He was very passionate about his work, especially now that it had the personal touch to it."

According to an online profile, James Durkin attended Princeton University, Rutgers University and Columbia University. The California Board of Psychology issued a license to him in 1990, but it expired in 2010, records show.

Durkin was known to drive around town in his old Mercedes-Benz. "He always looked wonderful driving," said a neighbor, Scott Sinclair.

"I'd like him remembered as a brilliant intellect," Sinclair said, "as someone who even in his retirement was deeply concerned for projects that would help others, and as someone who managed to keep active and involved at a very advanced age."