Gregory Allan Despres was born in July 1982 in Minto, New Brunswick, Canada. His early life was marked by instability; his parents separated during his childhood. He moved with his mother to Massachusetts, USA, where he initially led a relatively normal life, participating in community activities and sports. However, by his late teens, Despres began exhibiting signs of mental illness, including social withdrawal and erratic behavior. At 17, he returned to Minto, where his condition deteriorated further. He became increasingly isolated, often locking himself in his residence for extended periods and displaying paranoid tendencies. Despite his mother's concerns, Despres did not receive adequate mental health treatment.

On April 23, 2005, Despres forcibly entered the home of his neighbors, Fred Fulton, 74, and Veronica "Verna" Decarie, 70, in Minto, New Brunswick. He stabbed Decarie to death in the bedroom. When Fulton attempted to escape, Despres overpowered him, dragged him back into the house, and decapitated him with a homemade sword. Fulton's head was later found under the kitchen table in a pillowcase. 

After the murders, Despres crossed into the United States at the Calais, Maine, border crossing on April 25, 2005, carrying weapons, including a blood-stained chainsaw. Despite his bizarre behavior and possession of weapons, U.S. border officials allowed him entry, citing a lack of legal grounds to detain him. Despres was arrested on April 27, 2005, in Massachusetts during a routine check, which revealed he was due in court in New Brunswick for a prior assault charge.

Extradited to Canada on September 15, 2005, Despres underwent a series of legal proceedings. His first trial in 2006 was delayed due to his erratic courtroom behavior and was eventually halted after he was deemed unfit to stand trial. Following psychiatric treatment, he was found fit for trial in 2007. During his second trial, the court heard extensive evidence of his mental illness. On March 5, 2008, Justice William Grant ruled that while Despres committed the murders, he was not criminally responsible due to his mental state at the time.

Despres was confined to the Shepody Healing Centre, a secure psychiatric facility in New Brunswick. Over the years, he has remained institutionalized, with periodic reviews assessing his mental health and potential risk to society.