Just figured this out this last weekend. The bigger holes are 9mm and 40 cal, the dents are 22 that rounds couldn't penetrate both sides and the motherboard plate, so those look like inside out dents on the back side.
Lol your lucky your a cop, you could just get some random items from the Evidence room. Say a fully auto M4, or Mp5, or (if you have my dads luck) A .45 Tommy Gun. (FYW AmericanSensei, my dad had a fully auto tommy gun that he would go use, a show off to trade for drugs, to bust people that way. He said it was awesome to shoot)
Anyways, a nice auto gun, or a good 'ol block of C4