The U.S. Justice Department has started an investigation of the South Carolina Highway Patrol after dash-cam videos showed a trooper using a racial epithet and two other patrolmen ramming their cruisers into fleeing suspects, a federal prosecutor said Thursday.

"I've reviewed some of the videos, and based on that review, felt that it was appropriate to have our office involved," said Kevin McDonald, acting U.S. Attorney for South Carolina. "We will open a file like any other criminal case, and work with the FBI in their investigation, and then make prosecutorial decisions."

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Highway Patrol Col. Russell Roark and his boss, Public Safety Director James Schweitzer, resigned last month after a tape surfaced showing a trooper using a racial slur. "You better run," then-Lance Cpl. Daniel C. Campbell said to a suspect, using a derogatory term for blacks, "because I'm fixin' to kill you."

Campbell was reprimanded, suspended and ordered to undergo anger and diversity training, but Gov. Mark Sanford said he should have been fired.

This week, the Highway Patrol released two more videos showing troopers using their cars to ram fleeing suspects. In one of those tapes, Lance Cpl. Steven C. Garren drives after a black man on foot, striking him when he crosses in front of Garren's cruiser. The man flips over the car's hood and into high grass on the roadside.

"Yeah, I hit him. I was trying to hit him," Garren, who is white, can be heard telling another trooper.

Garren received a three-day suspension, which he has appealed. Another trooper who also ran down a suspect with his car was reprimanded and completed a stress management course, disciplinary records show.

Sid Gaulden, a spokesman for the Department of Public Safety, said none of the troopers were available for comment Thursday. He said the department welcomes the investigation.

"I believe that such an inquiry will prove the fact that there is no systemic pattern of misconduct at the Department of Public Safety," Gaulden said. "We saw problems and took action to correct those problems."

McDonald, the federal prosecutor, wouldn't say whether indictments could come from the investigation, which was first reported Thursday by The State newspaper of Columbia.