An ex-Marine and Iraq war veteran has been charged with murder for the stabbing of four homeless men to death in California's Orange County.

Police arrested Itzcoatl Ocampo 23, after he killed a 64-year-old man outside a fast-food restaurant in Yorba Linda. The victim was John Berry, believed to be a Vietnam War veteran who used to sleep along the bed of a river.

Ocampo was taken into custody when bystanders chased him down after the stabbing. He is expected to be charged with four murders.

"We are extremely confident that we have the man who is responsible for all four murders of homeless men in Orange County," Anaheim police Chief John Welter told Contra Costa Times.

Ocampo's father Refugio Ocampo told AP that his son came back mentally unstable from Iraq, where he was deployed in 2008. "They killed the person he was," he said. "He talked about the end of the world. Something big was coming. A big war."

Refugio Ocampo is a homeless himself, having lost the job and ending up living under a bridge and in a sem-tractor.

He told the Orange County Register that his son showed him reports of the stabbing last Tuesday. ""He was worried about me because homeless people were being killed," said the man.

Itzcoatl's family described a physical condition he suffered in which his hands shook and he suffered headaches. Medical treatments helped until he started drinking heavily, they said.

The younger Ocampo graduated in 2006 at Esparanza High School, and followed a friend into the Marine Corps instead of going to college.

At least 121 Iraq or Afghanistan war veterans killed someone or were charged with a homicide after returning home between 2001 and 2007, The New York Times reported. About three-quarters were still in the military when the crimes occurred.