Batman: Arkham Asylum Guide - Walkthrough
Batmobile Crime Scene
Your new objective is to scan the crime scene around your car, looking for clues as to where Harley may have taken the Commissioner. Trigger Detective Mode and note the outline that represents the Crime Scene – now get scanning!
It seems that the Commissioner left you a trial to follow! Before you get tracking though, notice the structural flaw marker by the building on the ground with the Riddler Statue beneath it? Now is a great time to test out the explosive gel, right? Head on over and, once you are on the flaw slab, hit LT and use RT to deploy the gel, then back off and hit RB to detonate it, giving you access to the Trophy, which you naturally grab now.
Back on the tobacco trail, you end up at a locked door – but fortunately for you the wall nearby looks weak – so hey, let's blow it up!
Pass through the door here and continue to follow the trail as it leads you through a gate, down a walk and up a flight of stairs. At the other end of the stairs is a group if unarmed prisoners for you to pummel before you follow the trail into the building here, where you encounter Harley Quinn behind a forcefield, with the Commissioner her prisoner.
After the CS in which Harley points out that you have to find an alternate route, head outside and then zip up to the roof above. Run towards the low upper ledge and jump up, and then follow that around to the left where you will find a weak spot in the nearby roof.
Using your explosive gel, blow open that spot and enter, dropping down into a room with lockers in it. There is a door here – go ahead and open it and pass through!