Brain Dead

Brain Dead is a murder-mystery side quest in the Fallout 4 add-on Far Harbor.

Quick walkthrough
Ezra Parker is the murderer. He killed Julianna Riggs and then using his voice modulator was disguised as her the whole time. Once you talk to all the suspects and Maxwell, accuse Julianna to discover the truth and defeat or work with Ezra.

(EDIT) Investigate and follow the red stains near the Ezra's body, it will lead to a Keith’s baseball bat, implicating him in the murder. In the dresser in Keith McKinney’s theater, there is also a love letter from his wife to Ezra. Turns out the red stains are red paint, also implicating Santiago Avida. After finding these clues, the player may confront either Keith or Santiago. The killer will be the first the player accuses. Concierge and Protecterons will help terminate the killer.

Bugs
It is possible for Pearl to become stuck at the elevators, without saying the line about them being out of order. Leading her away and letting her return did not fix it - currently it seems loading is the only fix.