A co-worker wants to shoot everyone *UPDATED*

So at work yesterday, this guy I work with was in a fit of rage. He's not a bad guy, by any means. He genuinely cares about work and wants to move up. He just had a child and is married, and seems happy. He's twenty eight or something like that, but his priorities aren't in line. He'd rather play video games than take care of his child. I'm not someone who can judge him, so I don't, but I recognize that he should consider his priorities. He's also a bit of a 'know-it-all' and when confronted about it said, "How am I a 'know it all?' A 'know it all' is someone who pretends to know everything but doesn't, when I actually do know what I'm talking about." That should give you a good idea of what kind of person he is. That being said, I really don't have any issues with him.

His fit of rage was caused by everything building up, pent up anger. He stormed in the back room, kicking the door open, and pushing everything out of his way furiously. Because I'm a caring person, I stopped him and I asked what was wrong, and tears were building up in his eyes. I could tell he was genuinely upset. He told me that he had been working all day on something, a task given to him by a manager, and when the manager came to check on him she asked him, "That's all you've done?!" He had worked very hard on this project. He told me that he felt disrespected and that he isn't ever treated fairly because he's regarded as a 'know it all' and only a few people there respect him. I told him that I respect him and he said, "It doesn't matter, because other than a few people, nobody listens to me because they think I'm stupid or something! I know what I'm talking about and I work hard but I get disrespected at every corner!" I tried to reason with him, saying "Dude, I understand...but we're in the same position as everyone else...they really don't have to listen to us because they're our peers. Just breathe and take a minute to calm down, don't take work so personally." Following this, he stormed off kicking more things.

A few hours later, I see him alone in an office crying while playing Animal Crossing, so I opened the door to see if he was alright. I told him, that I understand he's upset but he shouldn't let work anger him...it's just a job. He then said, "This isn't me angry, this is me upset. When I'm angry, you'll know. I'm going to ruin everyone in front of me someday, and I don't want you to get hurt if I do...you're a nice guy. I'd rather just shoot everybody than calm down. Nobody treats me fairly."

Now, at this point I told him he shouldn't say things like this...and I left.

I feel like I should tell somebody about this. He's generally not somebody who is taken seriously but this is kind of troubling. I care about too many people at work that, if something did happen I'd feel miserable...but I don't know if it's worth potentially ruining HIS life over, if he has no real intentions...because in all fairness he's somebody who wants to SEEM knowledgable and powerful.

I don't know what to do, especially considering I'm the only person (to my knowledge) that he's said this to. If I tell management and they confront him, he'll know I said something to them.

I just need some advice on this. I really don't think he's going to take any action.

EDIT: My most recent post in the thread has an update on the matter.