even though the girl did not know this, that guy is tied to 10 other robberies, thus they inadvertently stopped a very dangerous man from hurting other people.
Yes, They did risk their lives and the guy could have hurt them a lot more. But when she closed that door, maybe, I think,maybe... she just, didnt want to let the bad guy win? maybe her gut reaction was to stop a dangerous guy from getting away?
Can you imagine if all our superheroes thought the same way of what you said
"why stop the joker? insurance will save the bank" "why stop Green Goblin, the police need to do their jobs!"