A Tennessee man pleaded guilty to murder and child abuse charges Monday in the 2012 death of his 6-month-old daughter.

Investigators originally thought Atu Campbell's daughter was killed in a car accident, but new evidence suggested that was not the case.

According to the Shelby County District Attorney's Office, Campbell drove his vehicle off the intersection of Dove Street and Baskin Street in Frayser and struck a fence.

That happened on Oct. 25, 2012.

Police said Anyiah Nabors – Campbell’s daughter – was found face down on the floor of the backseat, and the baby seat was upside down and not properly secured.

An off-duty firefighter who witnessed the accident said Nabors had a faint pulse, but she wasn’t breathing, was pale and had a “stiff body type.”

>> Read more trending news

Investigators found later that the baby had injuries – including fractured ribs and a lacerated liver – that were “not consistent with involvement in a minor traffic accident.”

Campbell was sentenced to 20 years in prison without the possibility for parole for second-degree murder and aggravated child abuse.