FEDERAL HEIGHTS — A man claims a police officer broke his arm, left the scene without getting him help and then returned after the man called 911 — only to deny seeing him earlier.

Federal Heights police Officer Mark Magness, 45, who has been with the department one year, is now under a joint criminal and internal-affairs investigation but remains on the job.

Dennis Discua, 34, said he was walking home with his 3-year-old son after watching July Fourth fireworks on a nearby hill. Witnesses said Magness, who was on routine patrol, began to round up some of the spectators to ask them about reports of illegal fireworks in the area.

When Magness approached Discua, the man pointed to his house a few feet away and said, “I live there.”

That’s when Discua and five witnesses say Magness put out his foot, twisted Discua’s arm back and threw him on the ground.

Discua tumbled 20 feet down a concrete culvert, stopping when he hit a curb below, witnesses said.

His head and ear were bleeding, his shoulder was scratched and his arm was dislocated and fractured.

“I could see the bone was popping out of his elbow,” said neighbor Zach Davenport, 19.

Discua says he then showed the officer his injury.

“He got his flashlight and looked and sees my arm,” Discua said. “Then he just said to my neighbors and me, ‘Go home.’ And then he just left.”

Neighbors helped Discua to his front porch and then dialed 911.

The dispatcher sent the nearest officer — Magness — who returned and pretended not to know what happened, according to witnesses.

“The cop came down the street, and he got out of his car, and he said, ‘What happened?’ And he’s playing it off like it wasn’t him,” said neighbor Frank Brandin.

Magness can be heard on a dispatch tape when he was sent back for the second time referring to Discua as someone he met earlier in the night. He declined to talk to 9News, saying that he can’t comment because it is an ongoing investigation. Magness did deny pushing Discua down the hill or breaking his arm.

The witnesses and Discua said they are sure that the officer who injured Discua also responded to the call.

“Unless he’s got a twin brother that works for Federal Heights as a police officer as well and was on the job on the same night, it was him,” Brandin said.

The witnesses and Discua have filed police reports with the Federal Heights Police Department. Discua has hired an attorney.