Internal Affairs detectives are investigating a possible police brutality case after witnesses say several Denver officers pummeled a man in the face with their fists and kicked him in the side, breaking a rib while he was handcuffed and lying face down in an asphalt alley.

"I saw them hitting him in the back of the head. They were hitting him in the face and kneeing him in the side. That's how dirty it was," said Jeannie Ruiz, 49, a neighbor. "That was the worst thing I've ever seen, ever."

Other neighbors say police force was justified because the man, Ignacio Zepeda, 22, was fighting officers.

Two officers were taken to Denver Health Medical Center for treatment following the arrest; one was kicked in the knee and the other hit in the face.

Denver police spokesman John White said he could not comment about the arrest or the brutality allegations because Internal Affairs is investigating. He declined to release Zepeda's mug shot.

Zepeda was treated at St. Joseph's Hospital. He was arrested, police said, for investigation of first-degree and second-degree assault for a series of actions, starting at 5 p.m. Tuesday in the 1500 block of Xenia Street, that included throwing a brick at a neighbor and hitting, elbowing and kicking police.

Megan Zepeda, Ignacio's aunt, said she pleaded with officers to let her talk to Ignacio to calm him down, but that a female officer threatened to arrest her if she didn't back away.

Ignacio's rib was broken, one of his eyes was swollen shut, his nose was swollen to three times its normal size and he had bruises all over his face and neck, the aunt said.

The Denver Post