It's a common formula. It happened today, here in Albuquerque. It happens a lot. Here are some of the most infamous..which is to say, the ones where more than two people died. The dots on the map of fellows who "just" kill their girlfriend would leave very little white space. (and there'd be a tiny scatting of pink dots representing gals who killed their boyfriends. Usually because he abused her. Has there ever been a girlfriend murdered boyfriend just because he left her? I can't remember it.
When guns are allowed freely in society, there is nothing you can do to protect yourself from gun violence. Which is too bad. In a universe without the current interpretation of the second amendment, this kind of violence would be almost fully preventable.
And you can bet that a man who walked into a crowded office conference room intent on knifing his ex-girlfriend to death would not have been able to do it and would not be now wandering the streets of Albuquerque.
Instead...six dead, four wounded, gunman at large. What a tragedy.