It's a pretty decent cliffhanger. All we and Dick know at this point is that some files about the Graysons' murder were hidden in the Batcave. This could mean many things:
- There's something about the murder that Bruce didn't want Dick to know. - New information about the murder came to light, but Bruce didn't know what was up, and didn't want to tell Dick until he'd nailed it down. - Jason got into the Batcave at some point and hid the tape to screw with Dick's head. - Bruce lost track of the tape after the last time somebody trashed the Batcave, and it happened to skid under one of the memorial cases.
Personally, my pick on this one is that it's a Jason Todd mindgame.