CHILLICOTHE, Ohio (WTVN) -- The FBI has launched a federal investigation into an incident involving the Chillicothe Police Department.

Matt Mitchell was seriously injured when a Chillicothe Police officer body slammed him while he was in a holding area of the Ross County Jail. Video of the April incident shows that Mitchell was handcuffed at the time. He had been arrested for DUI and had become combative in the police cruiser before arriving at the jail.

An internal investigation by Chillicothe Police, the law director, and mayor found no wrong-doing by Sgt. Christopher Dubay.

"If an outside agency wants to come in and give an expert look by their department, in this case it's the Department of Justice, we'll welcome that analysis," said Mayor Jack Everson.

The mayor says he's only aware of the Mitchell incident being under investigation by the FBI. He believes the federal agency was contacted by Mitchell's attorney, Bret Adams.

"We did not initiate any investigation with the Department of Justice or the FBI," said Adams who believes this investigation is into more cases than just that of his client's.

"One doesn't get a call from the Department of Justice about an isolated case involving the violation of civil rights," Adams said.

Adams says Mitchell has more than $50,000 in medical bills and is being evaluated for brain injuries from the incident. He's hopeful that having an outside, independent look at the case will result in a different outcome than the internal investigation.

"It's really difficult to say that the investigation of the Chillicothe Police was fair in that it was done by their own department," he said.

Everson says the situation was reviewed by the officer that does training on take-downs who also deemed that nothing improper had happened.

"If there's something wrong with our procedures we want to become aware of them and adjust them," he said.

"I think it will bring credibility, ultimately, to the situation that it was handled right and that we did everything within guidelines and regulations," said Everson.

The FBI isn't commenting on the case because it's an on-going investigation.