BALTIMORE >> In a pivotal day in the manslaughter trial of one of six officers charged in the death of Freddie Gray, the defendant himself took the stand for more than four hours to try to convince jurors he is a reasonable and responsible police officer who didn’t do anything wrong on the day Gray was gravely injured.

William Porter’s trial is the first in the most high-profile and high-stakes in-custody death case in the city’s recent history, and whether jurors believe his testimony will likely be the deciding factor in determining the verdict. With no eyewitnesses and no unequivocal evidence as to how and when Gray suffered the spinal injury that killed him, the trial could come down to Porter’s word against prosecutor’s assertion that he “callously” disregarded Gray’s request for medical aid, and intentionally left him unrestrained and vulnerable to injury in the back of the transport van.

Porter was poised and calm as he testified in his own defense Wednesday, telling jurors he didn’t call an ambulance for Gray because Gray was alert, appeared uninjured and didn’t complain of any pain or wounds.

Instead, Gray only said “yes” when Porter offered to get him medical aid, the officer testified. Porter said he suggested to the van driver, Officer Caesar Goodson, that Goodson take Gray to the hospital because he knew a prisoner claiming injury would be turned away from jail.

But “I can’t tell Officer Goodson what to do,” Porter said when asked why he didn’t do more to ensure Gray went to the hospital immediately.

Porter, who was driving a patrol car, responded to calls for assistance at some of the van stops. Porter said that during the fourth stop, he went inside the back of the van and helped Gray, who was handcuffed and shackled, from the floor onto the bench. Porter said Gray wasn’t limp, and was able to support himself with his legs.

The fourth stop is crucial in Porter’s case because prosecutors say Gray was already injured by the time he arrived there and that Porter’s failure to call a medic contributed to Gray’s death. Defense attorneys say Gray was injured later in the ride.

“Freddie Gray wasn’t injured at stop four or five, it’s that simple,” Porter said. “Had he been injured, I would have called a medic.”

Prosecutors also say that by not buckling Gray into a seat belt during that stop, Porter was criminally negligent. The department requires detainees to be buckled up and the policy was updated just days before Gray’s arrest, leaving no ambiguity about whether a prisoner should be belted in.

Porter told the jury the wagon is “pretty tight” and said that of his 200 arrests involving the transport van, he has never belted in a prisoner.

Porter added that it would have been Goodson’s responsibility to buckle Gray into a seatbelt and he didn’t know if Goodson did so at the fourth stop because he left the scene before the driver closed the van doors.

Goodson faces the most serious charge stemming from Gray’s death: second-degree “depraved-heart” murder. His trial is next month.

As Porter spoke from the witness stand, facing the jury box, the jurors listened intently, some leaning forward and scribbling notes.

“He never made a complaint of pain or an injury,” Porter said. “In order to call for an ambo I need age, sex, location and complaint of injury. He wouldn’t give me a complaint of injury.”

Porter, who is also black, told jurors that when Gray was arrested, he overheard him screaming and mentioning something about needing an inhaler. When asked if Gray said he couldn’t breathe at the van’s fourth stop, Porter said, “absolutely not.”

Trial resumes Thursday.