Orange County prosecutors had prepared but not filed murder charges against Christopher Dorner for the deaths of the Irvine couple believed to be the first victims in his alleged rampage, the district attorney's said Thursday.

Prosecutors said they probably would have sought the death penalty for the slaying of Monica Quan and her fiance Keith Lawrence.

Dorner's alleged crime spree prompted a massive, multi-agency manhunt that came to a close Tuesday after a Big Bear-area cabin in which Dorner was holed up burned to the ground during a shootout. A charred body found inside was positively identified as Dorner on Thursday. 

Graphic: Who they were: Victims in the Dorner case

Orange County prosecutors said they gathered "extensive evidence," including Dorner's social networking pages, residences and cellphones, and executed "multiple search warrants." An arrest warrant was signed Feb. 6.

Two days later, O.C. prosecutors prepared a criminal complaint against Dorner, but planned to wait to file the documents until Dorner was taken into custody "in the interest of public safety, and for tactical and investigative purposes," a statement from the district attorney's office said.

"This decision was reviewed and discussed daily and the OCDA was prepared to file a case against the defendant on a moment's notice should he have been apprehended or new developments in the case deemed it appropriate," the office said.

TIMELINE: Manhunt for ex-LAPD officer

The complaint included two felony counts of murder, with special allegations of lying in wait and committing multiple murders, and a sentencing enhancement for the alleged personal discharge of a firearm causing death, officials said.

Had he been tried and convicted in the Irvine case, the minimum sentence would have been life in prison without parole, but the district attorney's office said it would have likely sought the death penalty.

The office noted that the police investigation and legal review of Dorner's alleged crimes were continuing.

FULL COVERAGE: Sweeping manhunt for ex-cop

Dorner was suspected in a string of killings that began Feb. 3 with the deaths of Quan, a Cal State Fullerton assistant basketball coach, and her fiance, Keith Lawrence, a USC public safety officer. Quan was the daughter of a retired LAPD official who represented Dorner at a disciplinary hearing that led to Dorner's firing.

According to a manifesto that officials say Dorner posted on Facebook, he felt the LAPD unjustly fired him, when a disciplinary panel determined that he lied in accusing his training officer of kicking a mentally ill man during an arrest. LAPD Chief Charlie Beck has promised to review the case.

While on the run Thursday, Dorner allegedly fired upon police in two incidents in Riverside County. One Los Angeles police officer was grazed in the head in Corona; shortly after, authorities said Dorner "ambushed" two Riverside police officers sitting at a red light in Riverside.

Officer Michael Crain, 34, was killed in the Riverside shooting, and his partner was seriously injured. The Riverside County district attorney's office announced Monday that it had filed murder and attempted murder charges against Dorner for those incidents. Dist. Atty. Paul Zellerbach said that complaint carried allegations of special circumstances that would have made Dorner eligible for the death penalty.

On Tuesday, San Bernardino sheriff's deputies were hit during the gun fight near Big Bear that proceeded Dorner's apparent death. Deputy Jeremiah MacKay was killed; the other deputy hospitalized.

Many said although they were relieved that the days-long rampage was probably over, the moment was bittersweet when thinking of those Dorner is alleged to have killed.

“We are relieved, freed of the sense of being a community that is not safe because there is a cop killer hiding in our little mountain town," said Big Bear Lake Mayor Jay Obernolte. "But there is also a great sense of anguish. It’s sobering to think of the sacrifices that deputies made in the defense of our community.”

This story was reported by Times Staff Writer Kate Mather.