When injustice aligns with cruelty, and heavy weaponry is involved, the results can be shameful and bloody. Witness what happened on Sunday in North Dakota, when law enforcement officers escalated their tactics against unarmed American Indians and allies who have waged months of protests against the Dakota Access oil pipeline.

They drenched protesters with water cannons on a frigid night, with temperatures in the 20s. According to protesters and news accounts, the officers also fired rubber bullets, pepper spray, concussion grenades and tear gas. More than 160 people were reportedly injured, with one protester’s arm damaged so badly she might lose it.

The confrontation happened at Backwater Bridge, on a highway linking the Standing Rock Sioux Reservation and Bismarck, N.D. Burned-out trucks and a police barricade have made the bridge impassable. Protesters say this is a needless threat to public safety — forcing emergency vehicles to detour about 20 miles — as well as a spiteful attempt to keep them away from the pipeline construction site. The violence erupted after some of the protesters tried to remove the truck carcasses on Sunday.

“We’re just not going to let people or protesters in large groups come in and threaten officers, that’s not happening,” said the Morton County sheriff, Kyle Kirchmeier. The Sheriff’s Department’s Facebook page linked to a video of the armed and armored officers, the water cannon drenching the crowd, and a rock flying overhead.