This trophy is titled "Baxter's Story" and it requires you listen to two things about Baxter at two different points in the game.
The first can be obtained after leaving the Regal Apartments when Ronan needs to go find the witness at the church. Ronan will be in an alleyway and you will need to walk down to the end to find two police officers talking. Possess one of them to hear a conversation to unlock Baxter and Ronan's Mutual Animosity.
The second is obtained once inside of the Salem Police Department. Once finished in the Bell Killer War Room, exit the room and proceed into the lobby. To the left of the main doors will be an event that needs to be revealed. Reveal it to obtain Baxter's Relationship with the Witness's Mother and the trophy.