Scott Dekraai, a man who was the suspect of last month's mass shooting at a salon in coastal town Seal Beach in Southern California, has confessed to the police he had pondered killing his ex-wife.

Dekraai quarreled with his ex-wife Michelle Fournier over the phone about custody of their 8-year-old son on Oct. 12.

After quarrelling, he drove to Seal Beach taking three handguns with extra magazines and ammunition and donning a bulletproof vest.

Initially, Dekraai spent time on the beach but he couldn't help wanting to seek revenge against Fournier.

His son Dominic sometimes came home with bruises, and he had photographed them, Dekraai told Seal Beach investigator Gary Krogman.

There is a journal documenting the dispute between Dekraai and Fournier, according to Dekraai's current wife.

Dekraai then drove to Salon Meritage where Fournier works, shooting Fournier and Christy Lynn Wilson, who had testified against him at a child custody hearing.

He also shot the salon owner, who rushed at him with scissors, and then fired at other five people, of whom four were killed, according to the statement by Andrew Stowers, a police officer in the nearby city of Westminster.

The 73-year-old Harriet Stretz was the only survivor in that shooting.

Dekraai then went outside and killed a man he suspected as an off duty or undercover police officer, who was reaching for a weapon when he shot him, according to Stowers.

Prosecutors are seeking the death penalty for Dekraai for his bloody and deliberate murder.

Fournier's friends have organized an event Dollars for Dominic on Saturday to raise funds to support Fournier's son Dominic.

Fournier's adult daughter from a previous marriage Chelsea Huff is Dominic's legal guardian and she is petitioning the court for full guardianship of the boy.