I think the shuffling of the crowd's feet trying to get out of there is what made the blood appear to be drag marks because concerts can be like that especially if there is a heavy crowd the flow of people can be brought to a snails pace, then throw a gunman with a suicide vest on top of that. That's my personal hell I've been to concerts that packed before and before the show is over I have to excuse myself because I get a tad claustrophobic, Lord knows what these poor souls had to go through to get out of there.