According to court documents, shooting suspect Scott Dekraai told investigators he argued with his ex-wife over custody of their son the morning of the shooting rampage.
When Dekraai was arrested shortly after the mass shooting last month at Salon Meritage, he told a police officer "I know what I did," according to an affidavit in support of a search warrant for Dekraai's home and vehicle.
Dekraai, 42, told a detective he and his ex-wife, Michelle Fournier, were involved in a custody dispute over their 8-year-old son.
"Dekraai indicated that his son ... would sometimes come home with bruises on his body. Dekraai would document the bruises in photographs," a statement of probable cause reads.
Dekraai told a detective after his arrest that he and Fournier had fought the morning before the massacre.
"After the verbal argument, Dekraai went home and armed himself with three handguns, extra magazines, and ammunition," reads the statement of probable cause.
Dekraai allegedly put on a bulletproof vest, got into his vehicle, went to Bolsa Chica State Beach and "pondered shooting his wife."
Documents say Dekraai then headed to the salon, immediately walked up to his ex-wife and shot her multiple times, then turned the gun on one of Fournier's friends who Dekraai said had recently testified against him in the child custody dispute.
The third to be shot, according to Dekraai, was the salon owner, Randy Fannin, who ran up to Dekraai armed with scissors.
Documents allege Dekraai then started shooting random people, viewing them as what he called "collateral damage."
When he left the salon, Dekraai said, he believed David Caouette was an undercover police officer reaching for his gun in an SUV. Dekraai killed him as Caouette sat in his vehicle.
District Attorney Tony Rackauckas has not commented further since an October news conference, when he said he would seek the death penalty against Dekraai.