A patient and I were in the middle of his session, he was talking and made no indication he was suicidal at all. In fact, he hid it very well because he hadn't made any indications of being suicidal the entire time I had been seeing him.
He was just talking away, and without any indication pulled a handgun out, placed it to his head and pulled the trigger. It happened so quickly there was no way for me to react, or try to stop him. I just picked up a phone and called emergency services. They showed up, and called it. I was interviewed, they went over everything and eventually ruled it a suicide and that was it.
His mother kept calling me for about 2-3 months before her husband made her stop. She was just an emotional wreck. I explained what happened, and that sometimes things like this happen. I was sorry for her loss, but there was nothing I could do for her.