Has there ever been a repeat mass shooter?
I don't have hard data, but probably not. Most probably don't get the chance. If they don't kill themselves and aren't killed by police, most of them are probably facing decades if not life in prison or even execution.
At least if we're talking about the sort of "classic" mass shooting scenario where a lone wolf type walks into a soft target like a school and opens fire indiscriminately.
If you open up the definition a bit, you might find some examples, though I don't really like doing that because they really seem like different kinds of scenarios to me.
You could probably find a couple gang or mafia types who have taken part in more than one incident where multiple people were shot. Same for certain terrorist/guerilla groups and such.
The beltway sniper attacks took place over about 6 months, though most of their attacks individually wouldn't count as mass shootings
After the Boston Marathon bombing the bombers shot an MIT police officer and then later had a shootout with police. Not mass shootings, and you could probably argue that everything that followed the bombing was just an extension of the original incident.
The shootings in Maine last year might count, since they took place at 2 different locations, but again you could probably argue that it was all part of the same incident.
That's what I can think of off the top of my head. Nothing that I'd personally feel comfortable labeling as "repeat mass shooter" but they are incidents that kind of lean in that direction that show that they may not be just one-off events and that the perpetrators may try to continue if not stopped immediately.
I feel like I've also seen a few cases where it was discovered that the shooters had plans to commit other attacks. We'll probably never be able to say conclusively if they actually would have followed through with those plans if given the opportunity.
