Just like in the case of the recent visit to the theater, the best method ids to attack the enemies staying in this area one-by one, while attempting to avoid detection at all costs, and using the smoke pellets, if necessary, to stage an escape. For moving around and quick escaping from the attack sites, use the numerous vantage points under the ceiling.
Just like before, you can eliminate the policemen in a number of different ways. Strategies worth attention are the attacks from above and inverted takedowns performed at the moment at which a enemy strolls under the vantage point currently occupied by Batman.
Another method which you have already learned is hiding in the tunnels under the bullpen. You can wait for the enemy in hiding and attack him straight away, or follow him to eliminate him quietly.
In the bullpen, there are no weakened fragments of the wall, where you could spread the explosive gel. Still, in one of the corners of the room, you should notice a weakened fragment of the ceiling. You can stand there and wait for an enemy to appear under Batman, after which you perform a (quite loud) takedown.
While securing this area, you can also use the gadgets that you have obtained recently. Especially useful here will prove to be the grapple, which you can use to pull the propane tanks or fire extinguishers towards the policemen, to stun or eliminate them from further action.
If you have purchased an upgrade for the grapple, called Heavy Reel Ammo you can also hoist the enemies up to string them up from vantage points. This technique works on a principle similar to inverted takedowns, but does not require you to wait for the opponent to appear in a given location. Unfortunately, by default, this attack can be activated only twice while clearing a given location.
After you have cleared the entire bullpen, jump down to the lowest level and go towards the Southern door. Activate the Cryptographic Sequencer here, and in the way that you have already learned, solve the hacking mini-game to determine the password (the screenshot).
[New Challenges: Custom Challenge]
Walk into the GCPD - Investigations and go South. When it comes to the two standard policemen that you bump into along your way, it would be a good idea to walk them from behind and perform a single special attack on them. After you reach the server room entry, try to break the security by using the Cryptographic Sequencer. This process will fail and you will have to obtain the disruptor from the evidence locker, as a result, mentioned earlier by the arms dealer.