[kijiki]

It's not common, but it absolutely happens: https://www.courthousenews.com/man-behind-s-f-system-lockout...

Early in my career in the mid 2000s, the startup that was on the same floor as mine laid off a QA person, who then showed up the next day and fatally shot the CEO and head of HR. Our CEO called me and told me not to come in that day.