Maybe the thugs were members from the BO and they have ways of knowing... Haha JK
It is suspicious that the... Wait! I think I get it!
How did the attendant get to the office with just an analogue watch with him? Unless the attendant lives at the office, which is extremely improbable, he would get to the office using the train too. And we know that trains collect fares from their passengers. He has no card, no 'proof of purchase' and no money with him, so how did he get there in the first place?
Did the boss tell the attendent that he was going to the office? Some bosses confide in their attendants and other bosses keep everything away from their attendants.
Say, even the boss is suspicious himself.