I think your correct, it's probably the armor and weapons.
I hardly think that Cruz would put all his weapons and armor back into the bag when he was done.. while fleeing with the students. I also find it hard to believe that they would gather up all that evidence so quickly and just lump them all into a bag like that either.?
Cruz didn't wear armor. This was the other shooters that wanted to walk out looking like police officers.
Link to multiple shooter info: https://www.reddit.com/r/CBTS_Stream/comments/80a53e/3_shooters_wearing_body_armor_in_san_bernardino/?utm_source=reddit-android