They're not serial killer at all, they're something else entirely. I'd say they are psychopaths (a person affected by chronic mental disorder with
abnormal or violent social behavior) or maybe more accurately they are a person who suffered a psychotic break. Where schools are involved there has been a ~20-30 year trend in defunding special ed, so those kids are forced into "gen pop" so perhaps that's were some of the school shootings come from. Perhaps the rise of SSRI can also be tracked back to this trend of defunding Special Ed and replacing SE with pills.
All that said, I still wonder why there is such resistance to any sort of regulation, such as licensing and registration. How ineffective are red laws going to be if we don't know who actually has guns? Killers are going to kill so we're going to make no effort to stop them because we can arm the entire population instead?