Four Marines, including one known as "Psycho," told investigators they robbed and murdered a fellow Marine and his wife last month after breaking into their home in search of valuables and sexually assaulting the woman, according to court documents.

The four were charged Wednesday with the execution-style slayings of Sgt. Jan Pietrzak, 24, and Quiana Jenkins-Pietrzak, 26, who were found gagged, tied and shot in the head on Oct. 15 in the living room of their home in Winchester, in Riverside County southeast of Los Angeles.

The home was ransacked and jewelry and other items were taken, investigators said. A fire was set, apparently in an effort to destroy evidence.

Two of the accused worked for Pietrzak, who was a helicopter airframe mechanic at Miramar Marine Corps Air Station in San Diego.

Pietrzak, who was born in Poland and raised in Brooklyn, N.Y., joined the Marines in 2003 and served in Iraq from July 2005 to February 2006.

His mother, Henryka Pietrzak-Varga, told The Daily News of New York on Wednesday that she had prepared herself for the possibility of her son dying in Iraq.

"But to die like this, in their own home?" she said. "They were good kids. They didn't deserve to die like this."

Murder charges were filed against Lance Cpl. Emrys John, 18, of Maryland; Lance Cpl. Tyrone Miller, 20, of North Carolina; Pvt. Kevin Cox, 20, of Tennessee, and Lance Cpl. Kesaun Sykes, 21, of California. They do not have attorneys yet.

John and Miller worked for Pietrzak. Miller said he forced his way into the home by pointing a shotgun at Pietrzak, according to an affidavit from a sheriff's investigator.

Miller said he and others went to Pietrzak's home to rob him, then tied up the couple and discussed with John whether to kill them.

Cox and Sykes, known as "Psycho," acknowledged they went to the home to rob Pietrzak. All four said his wife was sexually assaulted, the affidavit said.

The document also said that shoes found at the barracks where Cox and John lived matched prints at the crime scene, and that items believed stolen from the house were found at Sykes' home.

The men were each charged with two counts of first-degree murder and special-circumstance allegations of committing multiple murders, committing the crime during a robbery, and rape by instrument, district attorney's spokesman Ryan Hightower said Thursday.

John, who prosecutors believe shot the couple, also was charged with a special-circumstance allegation of using a firearm to inflict great bodily injury or death.

Sykes, who lives in the Fallbrook area in San Diego County, was arrested on Sunday. The other three Marines lived at the Camp Pendleton base and were held there until they were transferred to a Riverside County jail on Wednesday.

All were being held without bail Thursday. Their arraignment was postponed until Nov. 20. Prosecutors had not decided whether to seek the death penalty.

"Marines are supposed to be brothers," Pietrzak's mother told The Riverside Press-Enterprise this week. "What kind of brothers are these?"