BALTIMORE - The first of six officers charged in a police custody death that sparked riots in Baltimore went on trial Wednesday as a prosecutor focused on what the patrolman failed to do: Push a button to call for a medic who might have saved Freddie Gray's life.

Attorneys for Officer William Porter disputed this and other assertions made in the trial's opening statements, questioning how and when Gray's neck was broken in the back of a police van, and whether the young black man was really in need of medical attention when he first asked for it.

"You may hope finding him guilty will quell unrest," but Porter committed no crime, defense attorney Gary Proctor told jurors.

Porter was not initially involved in Gray's arrest, but he was there at five of the six stops the van made that turned a short trip into a 45-minute ride to the local police station.

Prosecutors said Gray told Porter he could not breathe and could not move from the floor of the van, where he had been placed head-first, in plastic handcuffs and leg shackles.

Gray's neck was broken between the second and fourth stops, which made his breathing increasingly difficult, the prosecutor said. He suggested the fatal injury could have happened when the brakes engaged, since Gray could not have used his hands or feet to brace himself.

"If it slams on its brakes, he's going to move at the speed it was going before it slams on its brakes," prosecutor Michael Schatzow said. "He's completely at the mercy of whatever happens."

Rather than call a medic, Porter picked Gray up from the floor and placed him upright but unsecured on the bench, despite Baltimore Police Department policy requiring a seatbelt restraint, he said.

Then, rather than take him directly to the station or a hospital, police made a fifth stop to pick up another suspect. By then, Gray was fatally injured, prosecutors said.

The defense attorney disputed the timeline, arguing that Gray was found slumped over on his knees by the fifth stop, so he could not have been already injured. "It's impossible. His legs wouldn't have worked," Proctor said.

Porter also suspected Gray had a case of "jail-itis" - police slang for feigning injury to avoid jail, his attorney suggested.

Porter "knew he didn't go quietly" during earlier arrests, so when Gray became more passive while still requesting a medic during van stops 4 and 5, the officer assumed he had simply exhausted himself rocking the vehicle early in the ride, Proctor said.

As for pushing the "talk" button on his shoulder radio to summon a medic, Porter's experience told him that could mean spending hours with Gray in an emergency room awaiting a doctor's note clearing him to go to jail, the defense attorney said.

Gray, 25, was picked up after running from police who were patrolling his neighborhood. A neighbor recorded a video of him being dragged into the van. He was unresponsive on arrival at the station, and was taken to a hospital where he died a week later, on April 19.

Porter, who also is black, is charged with manslaughter, second-degree assault, misconduct in office and reckless endangerment, carrying maximum terms of about 25 years in prison. He is expected to take the stand in his own defense.

The jury of eight women and four men was seated on the third day of a brisk selection process, given defense assertions that it would be impossible to seat an impartial panel in a city so convulsed by the case.

The other officers charged - two black and three white - will be tried separately beginning in January.