LAYTON, Mo. — Authorities said a man charged in the shooting of two police officers last week during a demonstration outside the Ferguson Police Department had attended the protest earlier that night, although multiple activists said he wasn’t a consistent fixture in their tight-knit group.

St. Louis County Prosecutor Robert McCulloch said Sunday in announcing the charges that 20-year-old suspect Jeffrey Williams told authorities he was firing at someone with whom he was in a dispute.

“We’re not sure we completely buy that part of it,” McCulloch said, adding that there might have been other people in a vehicle Williams is accused of firing from.

Williams is charged with two counts of first-degree assault, one count of firing a weapon from a vehicle and three counts of armed criminal action. McCulloch said the investigation is ongoing.

The police officers were shot early Thursday as a late-night demonstration began to break up following the resignation of Ferguson Police Chief Tom Jackson in the wake of a Justice Department report that found widespread racial bias in the police department.