Mental illness is at the heart of the recent back-to-back murder-suicide cases that left eight dead, including four children, in the San Diego area, according to experts.

Mental health professionals interviewed said murder-suicide is rare but draws a lot of attention because of the stories of horrific despair behind them.

"It's mostly untreated depression," said Dr. Rodrigo Muñoz, clinical psychiatry professor at the University of California San Diego and past president of the American Psychiatric Association. The most troubled develop what he calls "telescopic vision, where they get focused on a few things and forget the rest."

They're consumed by feelings of hopelessness and of living in a hostile world, he said. They become so irrational that they may feel they are saving their children from a cruel world by killing them.

Mary Alvarez, 41, who worked at San Ysidro High School; her daughter, Anjelica, 12; and son, Hamid, 11, were found strangled in their Chula Vista home on Wednesday. Police said they may have been killed by Alvarez's boyfriend, who is not the children's father.

Police have not identified him but he is believed to be the man who jumped to his death from a Spring Valley freeway early Wednesday. A friend of Alvarez told The Union-Tribune that she had recently moved to a new apartment to get away from her abusive boyfriend.

The deaths happened one week after the murder-suicide of a family in the San Diego neighborhood of Skyline. Police said Alfredo Pimienta, 44, and his wife Georgiana, 38, owned a towing business but were in financial trouble. The couple left a note indicating they planned the deaths of their daughters, Priscilla, 17, and Emily, 9, as well as their own. The bodies of the father and two daughters were found in a swimming pool and the mother in a bathtub.

Dr. Richard Shadick, director of the Counseling Center at Pace University in New York, said people who want to kill themselves usually give warning signs.

"Most notably, if someone has a history of violence they report feelings of depression, anger management difficulties, a sense of hopelessness and helplessness," Shadick said. "There is social withdrawal from the family, community and friends. Substances can be involved."

"Typically there are some difficulties that have occurred prior to a murder-suicide, financial difficulties, perhaps domestic violence," he said.

They're so far gone, Muñoz said, that they can't tell they're depressed and should get medical help.

"That's why we have to have campaigns for recognition of depression," Muñoz said.

It's unclear whether culture played a role in the murder-suicide cases. The Pimientas were Latino. Alvarez may have been Filipino and her alleged killer may have been Latino, according to authorities.

Latinos suffer from mental illness about the same rate as the rest of the population but are less likely to seek help, according to health experts. In San Diego County, Latinos make up one-third of the region's population but are just 20 percent of the adults who seek help at county mental health facilities.

"There is some shame associated with it," Shadick said, echoing a well-known cultural barrier. There is an expectation among Latinos, he said, that "men should be able to handle their problems on their own, that they should be able to make money for the family and handle marital or relationship difficulties without relying on others."

Dr. Ann Clark, a San Diego-based psychologist, said cultural and economic factors in the recent murder-suicide cases should not be minimized because of what can be learned to help prevent more tragedies from occurring.

Clark is chief executive officer at ACI Specialty Benefits, which provides counseling services to companies. She said employers usually provide counseling services for their employees. Free to low-cost counseling services are also available in various communities, she added. "Not ignoring warning signs is important."

Leonel.sanchez@sandiegored.com