COVINA, Calif. -- Police in California said the gunman who killed nine people at his former in-laws' Christmas Eve party had plotted the attack for six months.

They said he had also planned to kill his mother and his ex-wife's divorce attorney.

Covina Police Chief Kim Raney said 45-year-old Bruce Pardo left a rented vehicle near the attorney's home in Glendale the day of the shooting, but never made it back to the vehicle.

That day, Pardo put on a Santa Claus suit, entered the home of his ex-wife's parents armed with four guns and opened fire, killing nine people, then torched the house, police said.

He was burned and later killed himself at his brother's home.

Police said Pardo knew his mother had been invited to the party and intended to kill her because he felt she had sided with his ex-wife in their divorce.

Pardo's mother, though, had felt ill and decided to stay home.

Police said Pardo became increasingly desperate after a 2006 marriage failed, he lost his job and the family dog.

The slaughter came six days after Pardo and his ex-wife appeared in court to finalize their divorce.

Police said Pardo was severely burned as he torched the in-laws' house, and part of his Santa suit melted onto him.

They said Pardo had planned to flee to Canada but killed himself instead.

Hundreds of residents gathered Monday at a town meeting at a local school to begin coping with the attack.