First off, the blame for the murders is squarely on the shooter.
That being said, yeah, if someone egged him on I think they should get some punishment.
If the Sherriff knew his record of being violent, using drugs, making threats, & didn't do something toward preventing another occurrence, well, maybe the Sheriff should re-think his policies.
I know, they don't have to protect anyone not in custody. But with the alleged record of threats, isn't there some way he could have been put on a psych hold & evaluate?? Sounds like he might not have passed the test.