FULLERTON, Calif. -- Police should have been intimately familiar with Kelly Thomas and his history of mental illness.

Thomas had symptoms of schizophrenia and a 16-year string of arrests for everything from assault with a deadly weapon to public urination to jaywalking. But somehow, things ended differently this time.

Six officers who were trying to search Thomas' backpack on July 5 after reports of break-ins at a Fullerton, Calif., transit hub got into a violent fight with the 37-year-old. He later died of severe head and neck injuries.

His death has provoked outrage in the college town southeast of Los Angeles and raised questions about how well police in Fullerton and elsewhere are trained to deal with the mentally ill.

Across the country, there is no rule for how much training, or what kind of training, officers should undergo. Since the mid-1980s, increasing numbers of departments have put some officers through a special training program to learn how to diffuse situations involving the mentally ill.

These crisis intervention teams are often borne out of deadly incidents in which a mentally ill suspect dies in police custody or an officer is killed by a mentally ill person.

Fullerton officers frequently deal with the homeless because a major cold weather shelter is located in the city.

On July 5, Thomas was sitting on a bench at a transit hub where homeless people congregate, when the officers arrived. Police said he ran when they tried to search his backpack and resisted arrest.

A bystander recorded the incident with a cellphone. A bus surveillance tape showed agitated witnesses describing how officers beat Thomas and used a stun gun on him repeatedly as he cried out for his father.

The police department has called the case an isolated incident and put the six officers on administrative leave. The FBI and the district attorney's office are investigating the incident.