A man is dead after a four-hour standoff with Maine State Police on Interstate 95 in the Penobscot County town of Lincoln.

Police said the unidentified victim died of an apparent self-inflicted gunshot wound to the head from a rifle he was holding during the standoff. He was found inside his vehicle shortly after 8 p.m.

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The standoff began around 4 p.m. Monday, when police shut down a section of I-95 to deal with a motorist pulled over and allegedly threatening suicide. The man was in his vehicle, a U-Haul truck, with a gun to his head, police said. He was pulled over in the southbound lane just south of the Lincoln exit, and pictures showed his truck surround by numerous police vehicles.

Northbound traffic re-opened around 7:45 p.m., before the standoff ended. The southbound lane remained closed until 9:30 p.m., as investigators gathered evidence.

The U-Haul truck and the man and a woman inside it were being sought by police in connection with an unnamed missing persons case that police have been involved with since the weekend, according to Steve McCausland, a spokesman for the Maine Department of Public Safety.

McCausland declined to say who the missing person was and whether the person had been found, and also declined to elaborate on the relationship between the man and woman.

The woman left the truck shortly after it pulled over into the breakdown lane and has been interviewed by police, McCausland said.

He said more details will likely be released Tuesday, including the victim’s identity.