Investigate the situation in prison
You start Act 4 in the prison. There are no maps in entire facility, but in this guide you'll find hand-drawn maps, which should help you a bit. First mission is very easy - follow Mowen straight to the first bars (1) #1. A prisoner will tell you that both Titus as well as other prisoners sits in the canteen. Follow your companions until you reach double, red door (2) #2 leading to the canteen.
Once you get inside, a cut-scene activates, after which the quest is over.
The Green Mile
Obtained from: Titus Kabui
Difficulty level: Hard
Reward: 10000 Exp, Metal Kanabo
Free Titus' friend from his cell
You'll find Titus in the canteen's kitchen (1) #1 - talk to him. Your first mission to get to the Block C is to free and old Titus's friend, who can be found in the Block A. Of course it is full of undead so only you are able to complete this task. Leave the canteen and move to the entrance to the Block A (2) #2.
Once you get to the Block A (3) prepare for a tough fight with undead. There are also several "bosses" - watch out for a Ram #1 (4). This room is large enough to dodge his charges. In another part of the Block you'll find also a Thug (5). You have to go up the stairs to the third floor. A proper cell can be found with no problems - it is besieged by undead (6) #2.
Unfortunately the cell is locked so you have to go down the stairs to another floor #1. Be very careful here. At the very end you'll find the door leading to the control room #2, where you can open Alvaro's cell.
Unfortunately you've triggered the alarm. You have to switch it off as fast as possible because it attracts undead. A switch is located on the second floor #1, but you have to go to the other side, because the door in the control room is blocked. Once again go to the third floor and go with Alvaro to Titus. Once you leave the Block A, a Thug #2 will come out from a small room, which was closed till now. Your companion won't help you with the fight, so you have to defeat the zombie on your own. Now you can go to Titus and collect your reward.