Socks1000

Chosen answer: I don't think they experimented on him. He was too dangerous to have constant visit from anyone. So they just kept him locked up.

lionhead

Chosen answer: Caitlin was left in the possible future (where the virus had been released) when Peter teleported out. Then, when Hiro zapped the virus out of existance, that future became impossible, so that timeline became void. Basically, when that future ceased to exist, so did Caitlin, and since her parents seem to be dead (please correct me if I'm wrong, it's been a while seen I saw S2) and Elle killed her brother, there are no next of kin to raise awkward questions.

cherry_girl

Chosen answer: Because he's an idiot. From the story point of view, they needed the vault to actually be physically open so that the release of the virus would be a credible threat. Unfortunately, this required that Peter conveniently forget that he could simply walk through The Wall and use his telekinesis to tear the door open instead. Peter's increasingly large arsenal of abilities, where he ended up having pretty much any ability required for any situation, led to a situation where it became necessary to either have Peter apparently forget that he had a given power, as with the vault door scene, or become naively trusting, as with his refusal to scan Adam's mind to confirm his good intent. This problem, which simply made Peter look increasingly dumb as the show progressed, may well have been a key factor in the decision to severely reduce his ability during season three.

Tailkinker ★

Chosen answer: The German's powers could be limited in ways of heaviness of the metal he is manipulating. Meaning the door could be too heavy for him to rip off.

lionhead