The National Park Service has begun its investigation into whether a park ranger used excessive force in breaking up a party atop Acadia National Park's Day Mountain.

The park ranger, who hasn't been named, is accused of throwing a man to the ground after he'd been handcuffed, knocking the man out. Tim Wild, the alleged victim, says he was treated at Mount Desert Island Hospital for facial fractures he suffered in the fall.

The episode unfolded early on Aug. 18 when a group of 40 people, many of whom work at Jordan Pond House restaurant, made a midnight hike up Day Mountain. Rangers responding to a complaint issued citations for possession of marijuana and possession of alcohol by a minor.

Jill Hawk, chief ranger for the Northeast region, says park rangers who handled the Day Mountain incident remain on duty during the investigation.