This area contains Alliance quest NPCs Kharan Mighthammer and Marshal Windsor, as well as the Horde quest NPC Commander Gor'shak as prisoners. Their cell doors can be opened with lockpicking or other unlocking techniques, or with the Prison Cell Key which can be obtained from High Interrogator Gerstahn at the center of this area. The key is a white item which is always dropped, and can be picked up by any player with loot rights. It persists beyond the instance, so there is no need to kill Gerstahn for the key on subsequent trips, though she does drop decent loot. Note that the key is placed automatically in your keyring rather than in your bags.
If the players' goal is to free Marshal Windsor for his escort quest  , they should first clear the entire detention block of enemies. Once the quest begins, Windsor will walk through nearly every part of this area on his way out, leaving the players little time to heal and buff between encounters. In particular, clear out the locked store room on the west side of the detention block loop where Windsor's belongings are kept before starting the escort quest, as the event will spawn additional mobs in that area, making it a very difficult pull. Once Windsor steps out of his cell, he walks clockwise through the Detention Block halls, then across the large entry room, then clockwise through the Halls of the Law outside the Ring of the Law.
Access to the Dark Iron Highway and the East Garrison are found past locked doors openable with the Shadowforge Key. Access to the first part of the dungeon is granted only by defeating the challenge in the Ring of the Law.