Martin was sentenced to life in prison with the possibility of parole and has to pay restitution and court costs.
Two other men, Jonathan Askew and Michael Morris have already pled guilty to murder.
Martin also agreed to testify against the remaining co-defendant, Frankie Bradford.
Martin testified that he watched Bradford shoot Heard in the back of the head in a car in May of 2008.
He admitted he helped drag Heard's body out of the car and into the brush along County Road 3 in Chambers County, AL.
Martin also confessed, he helped cleaned up the blood stained interior of the car, drove home with the three co-defendants, and cleaned up the car once more.
When the district attorney asked Martin if he knew why Bradford killed heard, he stated, "Yes," and explained that he had a conversation with Bradford. He testified Bradford told him, he believed heard had gone to the police to snitch on his brother, who was allegedly involved in another shooting.
Officials tells us Bradford is the last and final co-defendant in the case. He is expected to go to trial next spring.
We're told the state is seeking the death penalty.