The suspect in a Seal Beach hair salon rampage that killed eight people pondered shooting his ex-wife after arguing with her over the custody of their 8-year-old son that same morning, court papers show.

A statement in support of a search warrant filed in Orange County Superior Court said suspect Scott Dekraai told an investigator he argued with Michelle Fournier by phone on Oct. 12, then took three handguns and extra magazines and ammunition, donned a bulletproof vest and drove to a nearby beach where he got out and pondered shooting her.

Dekraai told the investigator he then drove to Salon Meritage and shot Fournier and a woman who had testified against him in the custody dispute. When the salon shop owner rushed at him with scissors, Dekraai said he shot him, too, then fired at others who he saw as "collateral damage," according to the statement written by Detective Andrew Stowers.

Dekraai was arrested a short time later driving a white pickup and with three loaded magazines in his left leg cargo pocket, the statement said.

"I know what I did," he told the arresting officer, according to the statement that had previously been sealed and was made public this week.

The statement offers a first glimpse at the shooting from the perspective of Dekraai, who is scheduled to be arraigned Nov. 29 on eight counts of murder and one count of attempted murder.

Prosecutors are seeking the death penalty for Dekraai, 42, for the bloody rampage that rocked the tight-knit seaside community of Seal Beach. Orange County District Attorney Tony Rackauckas said he would not be surprised to see an insanity defense mounted by the Huntington Beach man who is being held without bail.

Authorities said Dekraai fired the shots seeking revenge against Fournier, who was a stylist at the salon. Dekraai shot eight people inside the salon, killing seven of them, then went outside and shot to death a man who was sitting in his car in the parking lot, prosecutors said.

Dekraai told the Seal Beach investigator he thought the man was an off duty or undercover police officer who was reaching for a weapon when he shot him, according to Stowers' statement.

In recent months, Dekraai had been trying to gain more control over his son's affairs and move him to a different school. But a court-appointed psychologist had recently weighed in on the dispute and recommended the former couple's shared custody arrangement remain the same, said John Cate, Fournier's attorney.

Dekraai, a former tugboat operator who was injured in an accident, told the psychologist he had previously been diagnosed as bipolar, Cate said.

After the shooting, police officers spoke with Dekraai's current wife at his home in Huntington Beach, who said she kept a journal documenting the dispute between her husband and Fournier. Dekraai told the Seal Beach investigator he had photographed bruises on his son's body that he came home with at times, according to the papers filed in support of the search warrant.

Authorities sought the warrant for Dekraai's home and his 2005 Toyota Tundra truck. Seven firearms were seized from his garage and three handguns were recovered from the pickup he was driving when he was arrested, the court papers show.

Authorities also seized computers and papers and photographs in a large envelope titled "Michelle Settlement Proposal 10/12/2011."

Dekraai's son has been in the care of Fournier's adult daughter from a previous marriage since the shooting, according to family court filings. She is seeking guardianship of the boy.