A man involved in a stabbing during demonstrations supporting President Donald Trump this weekend was arrested at the GW Hospital for simple assault Sunday, according to a Metropolitan Police Department report.

The MPD report states Corey Nielsen, a 39-year-old from Robbinsdale, Minnesota, was arrested at the hospital for his role in a knife fight that injured five people near Penn Quarter Saturday night. The report states Nielsen assaulted 29-year-old Phillip Johnson, a resident of Northeast D.C. who stabbed Nielsen and three other demonstrators, during the fight that was recorded in a New York Post video.

The stabbing was part of a weekend packed with violence and altercations among Trump supporters, counter-protesters and local law enforcement.

An MPD release states the suspects and victims engaged in an argument at the corner of 11th and F streets NW at around 9:00 p.m. Saturday, and tensions escalated into “a physical altercation.” The New York Post video shows a man push Johnson in the back, prompting Johnson to brandish his knife among a crowd of Proud Boys demonstrators.

Several individuals started pulling on Johnson’s face mask when Nielsen punches Johnson in the head multiple times, the video shows. The MPD report states officers located four victims with stab wounds when they arrived.

The report states officials transported Johnson, Nielsen and the three other stab victims to local hospitals following the altercation. D.C. Fire and Emergency Medical Services spokesperson Doug Buchanan told The Washington Post that some of the victims might have suffered life-threatening injuries.

Johnson was arrested Saturday night and charged with assault with a dangerous weapon, according to the MPD release. MPD officers collected the knife, an iPhone and two driver licenses at the scene, the report states.

The release states MPD detectives are working to identify the three other suspects in the case.

Nielsen and Johnson could not be reached for comment.