It's an awful story. He attempts suicide in March. Presumably he gets some sort of help, or maybe not. In either case, he then legally purchases a gun around April 17th (according to IMDb), and kills himself with it 15 days later.
As far as I know, background checks in CA are supposed to catch things like suicide attempts, but I don't know what the process was in 1990. Either way, he was granted a weapon that he should not have been allowed to receive. Was he even a US citizen?