To be honest, guys, they really didnt look like tourists....
The only thing that might have given it away was the map of New York that they had and the fact they spoke Japanese, THAT'S IT. Heck, sometimes I even need a map of New York and I live here. Two of the guys even got off the subway earlier then the rest, so they probably were from around here.
I didn't know anything about them, this was just an assumption from my observations.