Brain Dead

This quest starts automatically as soon as you enter Vault 118 and after talking to Maxwell. Follow him to the crime scene. Talk to Maxwell again and you'll have to search the scene for clues. First, examine the silver “blood” on the floor. Follow the trail of blood until you find the Fencebuster beside the red couch near the stage. Talk to Maxwell to discuss your findings. Your next step is to find and confront the killer.

First, talk to Keith Mckinney and ask him about his thoughts regarding the murder. Next, you have to investigate Santiago Avida. Follow the quest marker to find him in the reactor room. He'll start rambling about art and stuff so if you managed to convince him that you have the same interest with a speech check, he'll guide to a painting. You have to select whether you see a face or composition. He'll then lead you to another painting. You can choose whatever you want then finally he'll show you the painting for a kitty. Finally, you can ask him regarding the details of the case.

You'll get another lead to talk to Julianna Briggs next. She's with Bert Riggs, her husband. You can ask them both about the case to get another lead. Bert will mention something about the overseer's office. Head back to Maxwell and mention this to him. He'll tell you that the key to the Overseer's Office is inside Mr. Parker's room.

Head to the residential area and enter the room with the two lion statues by the doorway. You'll find the key immediately on the desk inside the bedroom. Now head back and go to the overseer's office. Once there, examine the overseer's terminal and read the logs. You can also eject the log and play it to get more clues.

After playing it, return to the room of the Briggs and talk to Julianna. Accuse her of the murder and the motive is embezzling. This choice will reveal the real murderer, no other than Ezra himself. It seemed he has killed Julianna then put up a ruse to pretend as Julianna. He'll convince you to let him go. You can destroy him outright, demand a pay cut, or tell him that you'll let him go. If you choose the latter, you can always go to Maxwell and tell him the results of the investigation. This will make the guards attack Ezra before he leaves the Vault. (Part of the short follow up quest, "Brain Dead 2")