Detective McDonnell was a good cop. Working the Boston Police rationing site, with his partner, Perry, McDonnell caught wind of a group stealing supplies intended for civilian distribution and selling them on the black market for a tidy profit. He pursued the leads vigorously, but found himself beating his head against the wall, as the Army did not allow him entrance. What's worse, the man responsible for the racket was the head of the unloading depot.
McDonnell apparently never learned that the perpetrators were his partner, Perry, and Sgt. J. Reise. However, his investigation caused Reise to become increasingly anxious. Unable to get rid of the detective or keep him away from snooping around the warehouse, he tried to set up a meeting with his partner in crime, but instead overheard Perry record a message for his cousin about selling Reise out. They shot each other soon afterwards.
McDonnell is mentioned only in Fallout 4.