One of my old housemates just returned to college to finish up his senior year in physics and could've found himself in an uncomfortable situation somewhat like that. He's a non-traditional student (age 30?) going to Eastern Kentucky Univ, where the physics department only has a little more than a half-dozen students per class, and he just found out that h'ed had a serious confrontation with one of the physics seniors (age 26, Iraq war vet) he'd have been sitting in class with.
It seems my housemate had a bad break-up with an ex-girlfriend and was going to punch out her new boyfriend (he later decked him in a bar), but she had one of her friends get this other physics major, who her friend claimed was a dangerous hit man, to intervene. So he an my housemate had a pretty intense little scene and my housemate stood his ground, being extremely belligerent.
Since then, the other student was arrested on multiple counts of murder, having partnered up with another Iraq war vet to go kill a guy who owed a local coke dealer $180,000. The guy's girlfriend and mother-of-two was at the guy's house, so they threw them both in a trunk, drove them into to boonies, and made them dig their own graves.
The physics major recorded the audio as the guy pleaded for his life and the life of his girlfriend. Then they shot her in the back of the head, cut the debtor's hands off (I suppose as proof), pulled out his gold teeth, and set him on fire, getting lots of nice screams for the iPhone. Then they dissolved the clothes in sulfuric acid, cut the bodies into little pieces, etc. One or both of them killed two more people in Berea, just to the south, and the physics major's partner had been running guns out of Chicago.
He got away with it for about a year, then the police were looking to pick him up so he sped to Louisville, where he turned on his iPhone just long enough for the police to get a ping off a cell-tower and swarm in.
So my housemate, who looks like a punk rocker and whose Facebook history is filled with references to drugs, says the teachers act a bit standoffish towards him, perhaps still shocked that the student they'd been teaching for three years was a hired assassin, so who else might be, or perhaps thinking that they've got another one in their class. The other students are a bit leery of him, too.
So last night he was asking me how he should handle it. I suggested that if they ask, admit he was in a serious, potentially deadly confrontation with the other student, but that it was over an ex-girlfriend, etc, and maybe the professors would open up to him a bit. It's quite possible they've already heard something about the previous confrontation from the ex-g/f's friends or other physics students, and are wondering if my ex-housemate is more violent and dangerous than the hit man was, because people gossip and exaggerate.
If nothing else, he could just whisper "If you cheat off me I will kill you and dump your body in a hole in the woods!"
BTW, the student's name was Daniel Keene.