... sounds to me they all knew whose keys they were and left them there
I have no feeling either way on this AA guy. But, as a former college dude myself, I can imagine being him and doing the same thing. You're leaving the bar, everyone is drunk, you see an acquaintance (LS), you pick her up/goof around/etc (she's okay with it), she's wasted, bar manager sees you, you then either let her go on her way or hand her off to another acquaintance/friend - all is well. I can easily see that happening. I can also see her keys dropping and nobody noticing. I can also see walking by later and putting them on the nearest fence to be found more easily by the owner.
This AA guy could be guilty as heck, I don't know, but nothing he's talking about is bizarre to me.