OAKLAND, Calif. -- As students at two Bay Area colleges mourned the violent death of a popular teacher, authorities Monday said the man arrested for the slaying had participated in an inner-city youth program where the victim had been a mentor.

However, Oakland police did not disclose the exact nature of the relationship between John Alfred Dennis Jr., 59, and Troy Thomas, 43. All authorities were willing to say to the San Francisco Chronicle was that Thomas had known Dennis since "his teenage years."

Oakland, police Lt. Ersie Joyner did tell the paper that Thomas had confessed to the crime.

Thomas was arrested late Saturday when a San Mateo County sheriff's deputy walked up to his car and asked what he was doing at Montara State Beach after 11 p.m. The deputy noticed an arm protruding from underneath a covering in the backseat and discovered Dennis' body.

When police ran the registration of the car, they found it belonged to Dennis. Thomas was arrested and a search of Dennis' Oakland Hills home revealed blood evidence of a violent struggle. Police believe that the popular teacher was killed there -- one of seven people killed in Oakland in unrelated incidents over the weekend.

"There was blood evidence," Joyner told the paper. "There was biological evidence. There was physical evidence."

Dennis was a popular teacher at both St. Mary's College in Moraga and the City College of San Francisco. On the St Mary's campus Monday, the room where Dennis' class on death and dying was to meet for the first time of the new semester was empty.

"For us, it's how do we cope," vice provost Francis Sweeney told KTVU.

Meanwhile, student Nitin Mathew remembered Dennis as a caring educator.

"He gave me his cell phone number to call him if I ever had any questions," he said. "Not many teachers do that."

At the City College of San Francisco, Dennis taught courses on American government, African literature, and race, gender and ethnicity. His students loving referred to him as "Dr. D."

The slaying remains under investigation.