Mike was meant to be helping record a weapon demonstration with the town watch, ordered by Ward at the East Mountain lookout. However, he paid little attention to the demonstration, preferring to work on a terminal. When another settler asked him to get off the terminal and help with the recording, he went to lock the terminal and then grabbed a rocket launcher incorrectly, causing it to fire and kill the other four settlers.
Upon realizing what he had done, he was mortified and fled to the nearby Kerwood Mine. He decided to hide out of guilt, believing that the others would view him as a murderer.
Supplying Demands: During this quest, it is up to the player to convince Mike to forgive himself for the incident and return to Foundation, as well as to return the rocket launchers he took to their rightful owners, the Brotherhood of Steel, or to kill him.
If he is spared, he mentions Ward thought it would be best if he is no longer on guard duty, so he helps out Foundation in other ways. He mentions he still has trouble sleeping at night.
If he is killed, the BOS weapons key can be obtained from his body. When reporting back to Gloria and Tad Chance, the player may choose to lie by claiming there was an accident with the weapons, lie by claiming Mike "went nuts" and killed everyone, or come clean about his death. This will affect the rest of the quest.
"I'm... Mike. Mike Tiller. Go to Foundation, tell them you found me dead. Because... I'm... I'm never leaving! I'm not going back, you can't make me! They'll never believe me... They'll think I'm a murderer!"
"They're too dangerous for anyone! They just... obliterated... so effortlessly... all dead. Look, I'll... Go back to Foundation, but I can't let you have these weapons. I'll leave... if you let me take the weapons back there myself."
"I mean, sure, but that doesn't change... what I did. How can I face them... after I... I... No... You're right. They should hear it from me. I'll go back... on one condition. Let me bring the weapons back myself."
The following is based on non-canon behind the scenes information.
Carl McKevitt was a contributor to Mike Tiller's design with the main goal of creating a character that the player could decide to kill or not.[Non-canon 1]
End of information based on non-canon behind the scenes information
Mike if he is encouraged to face everyone at Foundation
Mike if he is murdered by the player
↑Vault Dweller: "The Brotherhood doesn't 'make' any weaponry, nor sell them." Tad Chance: "Oh... Well. The stuff we got definitely has your logos on it. Some guys from the town watch took them out for testing a little earlier. I'm sure you can catch up with them, they normally practice at a small site they set up near the East Mountain Lookout, a bit North of here." Gloria Chance: "Oh that's right. Mike and them took the weapons out for a test drive. If you head over, I'm sure they'd let you take a look." (Tad and Gloria Chance's dialogue)
↑Mike Tiller: "H-h-hold it right there. Don't come any closer!" Vault Dweller: "Okay, okay, let's just take a deep breath." Mike Tiller: "No, you don't understand. What I did, I... Oh, man... I'm Mike. Mike Tiller. Go to Foundation, tell them you found me dead. Because... I'm... I'm never leaving! I'm not going back, you can't make me! They'll never believe me... They'll think I'm a murderer!" (Mike Tiller's dialogue)