Prosecutors are investigating the use of pepper spray and batons on spectators performing a haka at an American high school football game.
It was the first time Utah police had seen New Zealand's Maori challenge performed and they took action against the fans, including a dozen people from a single family, one aged 4.
This month, an internal investigation by the police of Roosevelt, 230km east of Salt Lake City, cleared their officers of misconduct in the October incident and said their actions were appropriate because they feared a riot was imminent.
But now, Deseret News has reported that Uintah County Attorney G. Mark Thomas has opened an investigation at the request of the Utah chapter of the American Civil Liberties Union, which claims the police report was "anything but objective".
The haka has become popular with at least a dozen American football teams at US high schools, especially those with large numbers of Polynesians.
On October 20, one Polynesian family drove 200km to Roosevelt to watch a relative play his final game for Union High School.
Union lost, to finish the season winless, and afterwards a group of Polynesian men and boys did a haka.