Luby's, 1991 IIRC Don't take the lack of publicity/common knowledge for lack of occurrence.

Considering how ruthless government is, and the litany of atrocities we actually know about done by our own government upon our fellow citizens since the 1940s, is it really so implausible that these ruthless bastards would seek out people who have a lot of mental issues, arm them and push them to commit mass public murder with the aim to influence public opinion towards certain ends? (Not every such instance is instigated by such shadowy people, but it is quite like some have been)