There were very few mass murders before 1970 when the government began to close the mental hospitals and dump the inmates on the streets. Semi-auto rifles were available since 1903. Yes, 1903! Yet the use of them did not skyrocket until the 1980s when the news media decided to go after rifles, something they said they would never do.
Almost every mass murderer since that time would have been a mental asylum as they have telegraphed their intentions ahead of time.
There were also NEVER mass murders in numbers before they started doping our kids up on psychotropic medications, teachers in schools used to be able to deal with kids that were hyperactive NOW the damn schools DEMAND the parents dope them up!!