Doubt these guys are "explorers". Why would they have a vial. Jim likes to rock climb, tune cars, dumpster dive, party, but probably not explore underground using a bolt cutter to break in. The chance that they were there just for fun is very slim, considering the risk involved.
BIG INFO: I just recalled that Jim is terrified of cops. I've gone drifting with him. He'll do a drift in a parking lot, then go on to another one. He's been caught by cops before and he's not big into getting into trouble. There's no way he was doing this for fun, he must have been doing it for some noble cause, or because he badly needed something inside that building.
Thanks for the extra info. I'm old -- what is drifting? Like snowdrifts? Don't laugh at me!
Oh, another thing ... do you think Chris was the leader of this little project, from what you know of the two?