A man was shot and killed Friday night in Nashua, according to the New Hampshire Attorney General's office and Nashua police.An autopsy showed Joseph Bisson, 57, died of gunshot wounds to his head and abdomen. His manner of death was homicide, according to the medical examiner. Officials said early Saturday morning they were investigating a suspicious death at a home on 56 Amherst Street. Investigators said they believe they have identified everyone involved in the incident but have not said if anyone is in custody. They said there is no threat to the public. Nashua police said they are investigating the shooting and the circumstances leading up to the incident. Anyone with information, including on Bisson's whereabouts in the hours before his death, can contact Nashua police at 603-589-1665.