Story highlights Sheriff: Itzcoatl Ocampo dies after falling ill at the Orange County Jail

His death is under investigation, including a pending autopsy

Authorities accused Ocampo of stabbing 4 homeless men to death

He was also charged in the deaths of his old friend's mother, brother

An Iraq war veteran accused of fatally stabbing four homeless men in Southern California is dead, authorities said Friday.

Itzcoatl Ocampo, 24, was pronounced dead the previous afternoon at Western Medical Center in Santa Ana, according to the Orange County Sheriff's Department. He had been sent there Wednesday from Orange County Jail, where he had fallen ill while awaiting trial.

Deputies noticed Ocampo "shaking and vomiting" in his solitary cell "and immediately summoned medical attention," the department said.

Ocampo was charged in January 2012 with four counts of first-degree murder . The first homeless man, killed a month earlier, was stabbed more than 40 times with a 7-inch, heavy-gauge Ka-Bar Bull Dozier knife, Orange County District Attorney Tony Rackauckas said.

"In each of these cases, the violence, the number of stabbing wounds of each victim, increased," the prosecutor added.

Authorities say 53-year-old Raquel Estrada was stabbed more than 30 times and her 34-year-old son Juan Herrera more than 60 times on October 25, 2011, their bodies left in pools of blood inside their Yorba Linda home.

The accused killer was being held without bail, with his next court appearance scheduled for January 17, 2014.

His death is under investigation "as is protocol for all Orange County Jail in-custody deaths," the sheriff's department said. An autopsy is tentatively set for early next week, with toxicology tests possibly coming back in several weeks.

Ocampo served in the Marines from July 2006 until July 2010, including a six-month stint in Iraq in 2008, according to military service records. He completed his service, with the rank of corporal, with the 1st Marine Logistics Group at Camp Pendleton, which is about 80 miles south of Los Angeles and 50 miles north of San Diego.

Friend: Ocampo 'down' after return from Iraq