>> reporter: according to the fbi, nearly 9 of every 10 museum heists have an inside component. rick abath who let the thieves in was interrogated for days. he also took lie detector tests. he was never charged with anything. and when we talked to him, he maintained he had nothing to do with the heist. and what about the regular night watchman who called in sick that night? rick remembers after he buzzed the thieves into the museum, they asked him if he was alone. >> i wonder if that -- are you here alone? because there were provisions for are a single guard to be there. i have wondered if "are you here alone" meant, do they get anybody to come in? but i don't know. >> reporter: but that night watchman, the one who called in sick, was never charged either. in fact, no museum employee has ever been charged with anything in connection with the crime. though investigators say no one