Officers responded to the 3300 block of Exposition Boulevard around 5:50 p.m. Sunday regarding reports of shots fired, according to the Santa Monica Police Department.
Two unharmed women and Arthur Tabuchi were found inside the residence when police arrived. A shotgun was discovered mounted on top of a workbench as officers investigated the garage, where they heard a voice, presumed to be Tabuchi's, threatening to kill someone, police said. They also found a spring-loaded firing pin with a wire attached to the end of the pin and the garage door.
"Officers determined the wire was set to pull the pin out of the housing and fire the shell toward the door when opened," the police department said in a statement.
A second shotgun was found next to a pedestrian gate on the north side of the residence, with a firing pin and trip wire set up similar to the one in the garage.
"This shell, which had been altered to be a sound diversion device (no projectile) had been recently discharged and is believed to be the source of the original shots fired call," police said.
A Los Angeles County bomb squad assisted SMPD officers in clearing the residence. No additional booby traps were found, and the shotgun shell in the garage was dismantled.
Detectives executed a search warrant for the residence and recovered other illegally obtained ammunition, police said.
Tabuchi was taken to a hospital for mental health evaluation and later booked on suspicion of assembling, placing, and maintaining a booby trap.
Anyone with additional information was urged to contact police Detective James McCoy at james.mccoy@santamonica.gov or Sgt. Shaun Cooney at shaun.cooney@santamonica.gov. The watch commander can be reached 24 hours at (310) 458-8427.