Zuma Press/Newscom

A man who had pleaded guilty to DUI manslaughter stemming from a crash near Tampa, Fla., on Christmas Day 2007 now denies causing the crash that killed three of the four people in the vehicle he hit.

David Belniak has sued the estate of Ray McWilliams, the now-deceased driver of the other vehicle, for more than $15,000, saying it was actually McWilliams who caused the crash by abruptly changing lanes, according to the Tampa Bay Times.

McWilliams initially survived the crash but later died. Belniak was sentenced to 12 years in prison, where he remains.

The money is to compensate Belniak for medical bills, "pain and suffering," and "loss of capacity for the enjoyment of life," according to the suit.

The Times reported that Belniak's attorney, Debra A. Tuomey, who is also his sister, said the government's prosecution amounted to a character assassination and Belniak accepted a plea deal only to avoid risking getting a life sentence in trial.

Tuomey said she wanted her suit, filed last month, to be considered alongside an existing suit brought by the victims' relatives against Belniak, scheduled for trial in April.

In an interview with ABC News, Maureen M. Deskins, who is representing the estate of Ray McWilliams, could think of no tactical reason that might explain Belniak's suit.

"If the jury [in the civil suit] decided McWilliams shared some fault for the accident, they would be allowed to apportion liability accordingly," she said.

Belniak's suit could backfire, she said, inflaming jurors, who might already be sympathetic to the victims of the crash for which Belniak admitted guilt.

"It's hard to wrap your head around," Deskins said.

"There aren't any facts that support the allegation [Tuomey] is making," Deskins added. "That's why the victims' family is breathless" at Belniak's suit.

Six eyewitnesses said McWilliams was stopped a red light when Belniak, at 70 to 90 mph, and never veering or braking, rear-ended him, Deskins said.

The event data recorder in McWilliams' vehicle showed it was not moving at the time of impact, she added. And prior to the incident, citizens had called Florida Highway Patrol to say Belniak had been driving out of control, she said.

Debra Tuomey did not respond to a request for comment.