02/21/2012 03:32 pm ET Updated Apr 22, 2012

Itzcoatl Ocampo, Accused California Homeless Killer, Pleads Not Guilty

LOS ANGELES, Feb 21 (Reuters) - An Iraq war veteran accused in the "thrill" killings of four Orange County homeless men and the stabbing murders of a woman and her son pleaded not guilty on Tuesday to six counts of murder.

Former U.S. Marine Itzcoatl Ocampo, 23, was ordered back to court on March 9 for a pretrial hearing in the high-profile case.

Meanwhile Ocampo's attorney, Randall Longwith, told reporters outside court that he was considering mounting an insanity defense on behalf of his client, possibly linked to his military service in Iraq.

"We're talking to as many family members as possible to determine a baseline as to what he was like before the war," Longwith said.

Ocampo was indicted last week on six counts of first degree murder, four of them stemming from the stabbing deaths of transients in December and January that rattled Orange County residents.

Orange County District Attorney Tony Rackauckas has accused Ocampo of carrying out those murders for a "thrill" and targeting victim John Barry after the 64-year-old transient appeared in a newspaper article about the case.

He is also charged with killing Raquel Estrada, 53, and her son Juan Herrera, 34, who were found stabbed to death in their home in October.

The victims are the mother and brother of Ocampo's high school friend, 24-year-old Eder Herrera.

Ocampo served in the Marines from July 2006 to July 2010 and was deployed to Iraq in 2008, according to the Marines. (Reporting by Dan Whitcomb; Editing by Paul Thomasch)