This is from January 1994.
From what little I gathered, in most cases is somebody who knows the place beforehand (worked there/knows friend or has relative, etc.) and that means they do not want witnesses left alive.
Here is another excerpt from the article:
There is no doubt that having a gun to defend yourself increases the odds of survival, especially if the bad guy does not know you have one (Hint: Nobody at work needs to know), but that does not mean you should surrender your life without a determined resistance. Yes, you may get shot, but it may not be the pop in the head he wants, and you may have a chance to survive.
Submission means an almost guaranteed death.