Dennis Gammill was Deputy Mayor of Malden in 2003. Five years before then, he had problems with alcohol and, on December 2, 1998, he accidentally hit and killed Darren Leveroni, a high school student, on his way home.
Gammill was so drunk that he didn't remember what he'd done, but realized it the next morning when he saw the front of his car. Since a witness had seen his car, he immediately got rid of it, and then doctored a list of similar vehicles sent to the police by the DMV, so his name didn't appear. In order to cover the reason why he wasn't using his car and instead using a rental, he claimed that his old car was stolen.
Gammill was so wracked with guilt that, during a city ceremony a few days later to bury a time capsule, he wrote a confession and dropped it in, expecting that no one would learn the truth for a hundred years. But, shortly thereafter, Mayor Rudner made a promise to Malden resident Miles Holling, the world's oldest man: if Holling lived another five years, the capsule would be dug up so a final chapter could be added to his life story.
Gammill joined Alcoholics Anonymous, sobered up, and tried to go on with his life. But when it looked like Holling would make it to the anniversary, Gammill panicked, fearing that his confession would be found if the time capsule was dug up. Gammill made late-night death threats over the phone at a payphone near the train station, trying to scare Holling to death. When that didn't succeed, Gammill killed a security guard, George Rowe, who worked at Holling's retirement home, stole his uniform and security pass, entered Holling's room, and smothered him with a pillow. However, on the night he killed George Rowe, he also ended up being bitten on the wrist by one of George Rowe's pet snakes, which eventually revealed what he did. He also, when writing out his pass, misspelled George Rowe's name, which eventually revealed what happened.
He made a few mistakes in regards to the murder, however: First, he closed the blinds before forcing Holling on the bed, something that Holling couldn't have done as his height would not have allowed him to reach the blinds, and the nurse did not visit him before the murder. Second, the method he used to murder him was to force him down on the bed and suffocate him, and made it seem as though he died in his sleep while reading a book, even though Miles Holling would not have used a bed to sleep precisely because he fears that once he uses a bed, he can never get up.
He was eventually found out by Leland Stottlemeyer. Though he denied everything, Mayor Rudner granted the police's request to exhume the time capsule, where Gammill's confession was found and read. Gammill was arrested.