So your friend came with the dude that allegedly jacked your BL2 disc. Seems like your friend isn't keeping with good company, so you should ask him to get the disc back from the dude. If he won't, he's not much of a friend.
If you want to beat him up... serious info here... first learn his routine, does he come home at night from work? Maybe he plays a sport, does he return from practice at night? Does he lived in a busy neighborhood? now... 1) buy a mask 2) buy some baseball gloves 3) get some sweatpants and a sweatshirt 4) buy said items at seperate stores with cash far from your house, the cops will ask stores if anyone has purchased those items together 5) remove tags and burn them from said items 6) put on gloves and use a hairbrush to scrub them off after putting them on 7) when you run up on to beat him up don't say anything as the cops will ask if he can identify his attacker by voice 8) have an escape route planned 9) burn said pieces of clothing. 10) have a solid alibi, maybe leave your xbox on and stay connected to xbox live, microsoft should be able to verify your story of, "I was at home playing my xbox) but make sure to rig your controller so u spin in circles or something to keep the "AWAY" status from appearing on your profile (idk how accurate microsoft tracks peoples' activity on xbox)
You should have gotten the cops to make him show them the install date on the game data file. If it was your copy he would have just installed the mandatory files and updates to play the game. If he had just bought the game he would still have the receipt or if he borrowed it from a friend said friend could vouch for him. It may not be open and shut but it would definitely lean in your favor.
Don't complain about a game having to much content that you can't focus. It's not the games fault you have the attention span of a squirrel.