I strongly recommend that you now acquaint yourself with the structure of the main hall in the Gotham Merchants Bank, because you will have to play another scene here which involves the elimination of the hostiles. For the time being, walk to the South. Ignore the locked door and turn towards the stairs on the left to find the venting shaft grate. Use the claw, and then the hook, to gain access to the venting shaft.
Walk through the tunnel and use the explosive gel right after you exit it, to blow up the unstable floor. You can now watch an important, from the plotline's standpoint, cutscene.
[New Character Profile: Joker]
[New Character Trophy: Joker]
[New Character Trophy: Bank Manager]