Factual error: In the arcade shootout, one of the replacement killers uses a Heckler & Koch MP5K hidden in a briefcase. However, he does not use the proper technique for this weapon. You should hold the case horizontally against your chest to be able to withstand the recoil. If you just walked & fired holding the briefcase at your side, you'd probably end up shooting into your own shin.
Factual error: During the scene when the main character is deciding not to snipe the cop in front of his children, the scope is on backward. The larger reticule is to the rear and the cap thumb release is to the front and on the wrong side. Not to mention that no self respecting sniper would chose a rifle with a CAR stock for a precision shooting. Not to mention a carry handle. Unstable long range system.