Finish all the Hostages Situations
After you capture a Garrison, either a Predator Path Quest or a Hostage Situation (or sometimes even both) will become available to start in that Garrison. For this particular trophy, you need to finish all of the Hostage Situations. All you have to do is go to the marked destination on the map and kill of all the enemies without alerting them, then go to the scientist and speak to him by pressing . If you alert any enemies, they will begin shooting the hostage, which will eventually lead to you having to restart the quest.