Cell phone video shot by a bystander shows how a white police officer in Wisconsin repeatedly punched a black teenager in the face. Police in Wauwatosa, Wisconsin responded to a call from security at Mayfair Mall on Friday that reported five disorderly teenagers. An officer was able to spot several of the teens in the mall parking lot and attempted to speak to them, according to a statement from the police.

The cell phone video shot by a bystander shows how a security guard was struggling to hold on to a teenager before an officer violently punched the teenager in the face. That makes the teenager fall to the ground, at which point he is again punched multiple times. “Why’d he punch him like that?” a person can be heard saying in the video. “Ain’t he a minor?” The man who shot the video said he immediately knew that kind of violence was inappropriate from a police officer. “I knew it was wrong, that punch was wrong,” Tyrone Jackson said. “If it was just a tussling, trying to get him down, okay that would be something different. But the punch to the face, twice, to a minor, it was something serious to me.” Police arrested a 17-year-old male, who was cited for disorderly conduct, battery and resisting an officer.

Police have vowed to investigate the incident but insist the video only shows a small portion of the interaction between the officer and the teenager. Law enforcement officers are reportedly reviewing additional video that supposedly shows how the teenager began to fight with the officer when he tried talking to him. “I can assure you that we take all situations seriously when they involve a use of force by our officers,” Wauwatosa Police Chief Barry Weber said in a statement. “We thoroughly review all incidents in which force is used by an officer and will do so in this incident, as well.”