Longtime Portland Press Herald editor and columnist Michael D. Harmon died of a single gunshot wound to the neck, the state Medical Examiner’s Office said Friday.

Harmon was killed at his Sanford home Wednesday. He was showing a handgun to a teenage visitor when it went off as the 16-year-old boy handled it, police said.

The boy and his father, who was present at the time of the shooting, are not related to Harmon, Department of Public Safety spokesman Stephen McCausland said Friday.

Harmon knew both of them “for many years,” McCausland said. The shooting will be reviewed by the Maine Attorney General’s Office.

McCausland said the boy and his father, both from North Berwick, have been cooperating with the investigation. Their names and details about the incident are not being released because of the ongoing investigation, he said.

A relative reached at Harmon’s home Friday said the family would have no comment on the shooting.

On Thursday, Harmon’s wife, Margaret Harmon, declined to discuss details of the shooting, calling it an “accidental tragedy.”