More witnesses are scheduled to testify in the defense of one of six officers charged in the death of Freddie Gray, the black man who died after suffering a spinal injury in the back of a police transport van.

Officer William Porter, who is also black, faces manslaughter, assault, misconduct in office and reckless endangerment charges stemming from Gray's death.

Prosecutor say Porter is partially responsible for not calling for a medic when Gray indicated he needed aid, and for failing to buckle Gray into a seat belt.

Porter took the stand for more than four hours Wednesday. He told jurors he didn't call a medic because when he saw Gray, Gray wasn't injured. He also said it's the van driver's responsibility to make sure prisoners in custody are buckled in. Porter wasn't driving the van.

Trial resumes Thursday.