Climb down the stairs. After you reach the locked door, select the explosive gel from the inventory and use it to blow up the weakened fragment of the wall on the right. Take the new passage, land onto the roof of the moving elevator and wait for it to reach one of the lower levels in the precinct. Grab onto a ledge and start circling the precinct's main hall [CPD - Bullpen], which you will be able to explore more thoroughly later on in the game. Along your way, remove the venting shaft's grate and listen to Captain Gordon's speech. Reach the end of the shaft and perform a quiet takedown on the nearby enemy.
[New Character Profile: James Gordon]
After you listen to the conversation with Alfred, start your exploration of the SWAT - Storage Room, which ill take to you to the SWAT - Manager's Office. In the neighboring room, there are three unarmed SWAT team members and you need to deal with them (it is a good idea to launch a surprise attack that e.g. assumes using the concussion detonator). After the fight finishes, locate the venting shaft's grate under the ceiling and rip it out, using the claw. Then, use the hook to reach the shaft.
Approach the SWAT - Conference Room and listen, along your way, to Branden's speech, which concerns the plans of capturing the Batman and collecting the reward set by the Black Mask. After you reach the ledge located above the conference room, select the hook from the inventory and aim at the point that you can see in the distance. Jump onto the rope and walk over it to the other side, and land safely in the room neighboring the one with the SWAT members.
[New Character Profile: Branden]
Move ahead and pass the room with the opponent group at a safe distance. Sneak up to the single enemy from behind here and perform a quiet takedown. After you do, turn to the door on the right, which leads to the reception desk. Select the Cryptographic Sequencer and start hacking into the local control panel, which will lead to the password being determined (the screenshot). You can now walk into the SWAT Division room.
After you walk into the next location, Batman should automatically hide behind a cover. Follow the game's suggestion and use the hook to pull the fire extinguisher towards one of the enemies. There are two upsides to this solution - this will lead to inflicting damage to the character that the extinguisher collided with, and will also allow you to blind the enemies temporarily. Use the momentary advantage in the best way you can, and start fighting right after using the abovementioned gadget. After you have secured this area, take the door to the SWAT - Interrogation Room].
Approach the one-way mirror and perform a quiet takedown on the policeman who is interrogating the acquainted arms dealer Ricky "Loose Lips" LeBlanc. After that, jump into the interrogation room and press the appropriate key/button to obtain valuable information from the dealer. Thanks to this you will learn about a gadget called the Disruptor, which is currently being stored in the evidence locker. Exit the interrogation room, and continue along your path for the SWAT Division.
[New Character Profile: Ricky "Loose Lips" LeBlanc]
[New Character Trophy: Ricky "Loose Lips" LeBlanc]
Once again, go towards the reception desk and use the hook to hoist yourself up above the largest group of the policemen who gathered here. It is a good idea to start also this fight using the grapple to pull one of the propane tanks towards one of the policemen (best at the one wearing a better armor) and to cause an explosion. Additionally, perform an attack from above and start fighting in a more conventional way, which is not going to surprise you anymore with anything new.
Once the fighting is over look for a barricaded window which separates the main hall from the side room. Use explosive gel here and detonate it so that you'll unlock access to the next area of the police precinct. Begin sneaking here, because this will allow you to surprise a cop who is talking on the phone.
rip out the venting shaft's grate and follow the corridors [Maintenance Access], while listening to the between Captain Gordon and his daughter Barbara. force another grate open and use the hook, and reach the ladder, thanks to which you will reach the GCPD - Bullpen occupied by eight armed policemen.
[New Character Profile: Barbara Gordon]
[New Character Trophy: Barbara Gordon]