Brain Dead

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

Quick walkthrough
SPOILER ALERT!!! Do not read if you want to solve the mystery yourself.

Ezra Parker is the muderer. 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.

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.