SANTA ANA, California — A 23-year-old Iraq War veteran charged with the stabbing deaths of four homeless men in a rampage that terrorized Southern California had selected additional victims, prosecutors said Tuesday.

Former Marine Itzcoatl Ocampo chose the final victim because the man appeared in a news article about police warning homeless men to be careful, Orange County District Attorney Tony Rackauckas said.

All four victims were stalked, and the killer looked for the right opportunity to execute them, he said. At least three of the victims were stabbed more than 40 times.

The district attorney said a panel will be convened to decide whether to seek the death penalty.

The charges include special allegations of multiple murders and lying in wait and use of a deadly weapon. The minimum sentence if convicted is life in prison without parole.

Rackauckas said prosecutors have no indication that Ocampo is mentally ill.

"It will be proven that the defendant planned all of his murders in advance, that he stalked his victims, that he looked for the right opportunity to execute them," Rackauckas said.

Ocampo's family said he was a troubled man when he returned from Iraq. Ocampo's own father is also homeless.

The killing spree began in December, raising concerns that a serial killer was preying on the homeless. Police and advocates then went on nightly patrols to urge them to sleep in groups or seek shelter.

Police arrested Ocampo when bystanders chased him down after 64-year-old John Berry was stabbed to death outside a fast-food restaurant in Anaheim, about 26 miles (42 kilometers) southeast of Los Angeles.

Anaheim Police Chief John Welter said Berry had filed a report with authorities saying he believed someone was trying to follow and stalk him. Welter said, however, that authorities were working through nearly 600 leads and tips but had not gotten to that report.

"It is unfortunate that we didn't get to him before the suspect did," Welter told reporters.

Rackauckas said Ocampo had twice gone through motorist checkpoints set up by police to seek potential information about the killer from members of the public, but there was nothing that drew their attention to Ocampo.

The weapon was described as similar or the same in each of the killings — a 7-inch (18-centimeter), single-edge blade made of heavy gauge metal.

The blade went through bone without chipping or breaking the blade, Rackauckas said.

Ocampo is being held in isolation in an Orange County jail, is wearing a protective gown and is being monitored 24 hours a day, said Jim Amormino, a spokesman for the Orange County Sheriff's Department.

"Obviously he has some psychological problems just by the nature of the crimes, so they don't want him to hurt himself," Amormino said.

Ocampo's father, Refugio Ocampo, said his son was deployed to Iraq in 2008 and came back a changed man. He said his son expressed disillusionment and became ever darker as he struggled to find his way as a civilian.

After he was discharged in 2010 and returned home, his parents separated. The same month, one of his friends, a corporal, was killed during combat in Afghanistan. His brother said Ocampo visited his friend's grave twice a week.

Like the men Ocampo is accused of preying on, his father is homeless. His father lost his job and ended up living under a bridge before finding shelter in the cab of a broken-down big-rig he is helping repair.

Just days before his arrest, Itzcoatl Ocampo visited his father, warning him of the danger of being on the streets and showing him a picture of one of the victims.

"He was very worried about me," the father said. "I told him, 'Don't worry. I'm a survivor. Nothing will happen to me.'"