FBI agents and police from Costa Mesa and Long Beach searched El Dorado Park with cadaver dogs for two days before finding the head thought to be Samuel Herr, 26, on Saturday, Costa Mesa police Sgt. Patrick Wessel said.
An arm and hand were found at the park Friday, and authorities had said the head was the only body part still missing. A coroner will officially determine whether the remains were Herr, Wessel said.
Herr's Costa Mesa neighbor Daniel Wozniak, 26, is accused of killing and dismembering Herr and killing Herr's friend Juri Kibuishi for money.
Wozniak was charged with two counts of murder Friday, just hours before he was scheduled to get married in another Long Beach park. He was being held without bail Sunday at Orange County Jail. No arraignment date has been set.
Investigators believe Herr was shot and killed in a theater at the Los Alamitos Joint Forces Training Base. His torso was found in the theater's attic May 21.
Authorities have not said why the two were at the base. However, Herr was an Army veteran who had served in Afghanistan, the Los Angeles Times reported Sunday. He and Kibuishi were both students at Orange Coast College.
Authorities allege Wozniak shot Herr, then cut off his head, left arm and right hand. Investigators said Wozniak told them where to find the torso.
Wozniak also is accused of shooting Kibuishi after summoning her with a text message on Herr's phone. Authorities believe Wozniak removed Kibuishi's clothes to fake a sexual assault. Herr's father found her body in Herr's apartment May 22.
Wozniak, a stage actor, had recently appeared in the leading role in the musical "Nine" at the Hunger Artists Theatre Company in Fullerton. He had money problems, and police believe the motive was financial.
Wozniak had been scheduled to marry one of his "Nine" co-stars Saturday.
Police detained a 17-year-old boy after he withdrew nearly $2,000 from Herr's bank account, money the boy said was for Wozniak, Costa Mesa police said. The boy's name was not released because he is a minor, and it was not clear whether he would be charged with a crime.
Wozniak's father, Daryl Wozniak, said his son tried to commit suicide after his Wednesday arrest and was treated at Western Medical Center.
Daryl Wozniak said his son never showed any violent tendencies or psychological problems but stopped accepting his phone calls six months ago.
Two other people, Noah Buffett, 28, of Long Beach and Daniel Wozniak's brother, Timothy Wozniak, were arrested for investigation of being accessories after the fact.