Great scene with the night / thermal vision staring on the monitor, but how did they know the gang was gonna be there? I have seen this film a few times but on the latest viewing I seem to have missed something.
Remember when Hannah says "when they walk out of whatever score they are going to take next, they are going to have the surprise of a lifetime". That was because once they had identified the gang they had them under constant surveillance and knew what places they were looking at. They most likely tailed them to the metals deposit then the day of the heist staged in the back of the truck for the arrest.
I had assumed this was the case, I guess it's really the only explanation. I thought maybe they had got the info from someone they had forced into becoming an informant or something.
They were surveilling the gang after they made a link with the witness to the armored van heist saying they heard someone say slick, "Slick" and putting Tom Sizemore's character with that nickname following corroboration from an informant.