Replying to NS i need dog help

So my family has two dogs, one (Steve) we've had for a little more than a year (since he was a puppy) and another (Jim) whos like ten months old we've had for five months.
Recently (last night) jim attacked steve and it was a shit show.  today he attacked him four separate times.  Like crazy dog fight attack, i got bit and shit, its not good. So my question to NS is this, any experience with this type of thing where a nice dog snaps and goes bloodlust on his best dog-friend's ass? 
By the way Jim is a pit lab mix and steves a retriever lab mix. good input wanted. thanks all