When you visit the interrogation room you will find that it is covered with weird pictures of clowns. Speak with the man here and he will introduce himself and give you a quest to find 8 posters of him that are placed around the town. This guide will show you all of the Mr.Adams poster locations in The Fractured But Whole.
You should try pick this quest up sooner rather than later. Most of the posters, if not all of the posters are easy to find. You will likely find the locations of all of them as you adventure around South Park. You will usually find the poster hanging on some kind of notice board. The bottom of the poster will be torn off and you will just see his eyes. Go up to the poster and press X or A and it will replace this poster with a new one. This is all you need to do.
This video guide from PowerPyx will show you where to find all of the Mr.Adams posters in South Park. Once you have found them all, you can head back to the police station to claim your reward.