Authorities’ tentative conclusion is that Jeffrey Alan Lash was a rich eccentric so caught up in his make-believe world of spying that his fiancee believed it, too

Inside his own head, Jeffrey Alan Lash was a secret government operative under constant surveillance by the CIA, the FBI or both.

He spent lavishly to build up an arsenal of 1,200 firearms, six and half tons of ammunition and explosive-making materials, which he piled high in every room of the small condominium he shared with his fiancee in a well-heeled hillside enclave high above the Pacific Ocean in Los Angeles.

He had twelve cars, including one reported to be bullet-proof and worth around $100,000. When he and his fiancee went to dinner at the local Italian restaurant, they drove in separate cars, and always paid in cash.

Any time Lash saw a camera, he would get upset. He told people his name was Bob Smith. Then he died, and things got truly strange.

Police in Los Angeles have spent several days figuring out why Lash’s body ended up in a car outside his house and was left to decompose for almost two weeks. They found it last Saturday – not because of a tip-off from the neighbours, who appear to have been oblivious throughout, but because a lawyer representing his fiancee gave them a call.

They also deployed a bomb squad and chemical experts in Hazmat suits to go through his vast arsenal of weapons and explosives – all of it, to judge police photographs and initial reports from the investigation, acquired legally and left untouched.

Some chemicals were too unstable to transport, so the police blew them up. The tentative conclusion is that Lash was a rich eccentric so caught up in his make-believe world of spying and derring-do that he had his fiancee, Catherine Nebron-Gorin, convinced it was real.

When he was diagnosed with cancer a year ago, he reportedly told her it was the result of chemical weapons exposure on an old mission.

On 3 July, the couple and a friend were shopping at a supermarket in Santa Monica, a few miles away from the house, when Lash became unwell and died in the outdoor parking lot.

Nebron-Gorin later told a friend she had specific instructions from Lash on what to do if he died. Don’t call the authorities. Leave him in a car. Get out of town, and let his minders take care of the body. So she did that.

The friend, a doctor who did not want to be named, told the Palisadian Post newspaper he spent 90 minutes trying to revive Lash in the passenger seat of an SUV outside his house on the night he died as Nebron-Gorin was “wailing and grieving”.

Nebron-Gorin left for Oregon and when she returned she was stunned to see Lash’s body where she had previously left it. She called a high-profile criminal defence lawyer, Harland Braun, whose previous clients have included Dennis Rodman, Roseanne Barr, Gary Busey and Robert Blake, the actor eventually acquitted of murdering his wife in circumstances almost as bizarre as the Lash case.

Braun told the police about the body and warned them the house was stuffed with weapons. And the police immediately evacuated the neighbourhood.

Lash grew up in a modest home near the Los Angeles international airport and had ambitions at one point to become a microbiologist like his father. Then, according to his stepmother, he largely cut himself off from his family and became secretive about what he was doing. “He was just a loner, as far as we were concerned,” Shirley Anderson told the Los Angeles Times. “He just became weird because he changed all of a sudden.”

There was no immediate explanation of how he obtained his money or what, if anything, he had done for a living. According to police estimates, Lash spent at least half a million dollars, and perhaps more than twice that, on his weapons stash. The condominium, which is in Nebron-Gorin’s name, last sold for $440,000 in 1991.

Braun, the lawyer, said he doubted the story about working for the government was true. “Whether he really was working undercover for some government agency or not,” Braun told the Palisadian Post, “he was convinced he was and he had my client convinced.”

Lash’s neighbours said they too were told Lash had worked for the CIA and found him odd. One employee of the Casa Nostra restaurant said Lash and Nebron-Gorin had eaten most of their meals there for the past seven years. Invariably, Lash would order raw filet mignon.