The trial of William Porter, one of six Baltimore police officers charged in the death of Freddie Gray, is now half over: the prosecution rested its case after five days of testimony and the defense is poised to begin calling witnesses Wednesday morning. Porter faces manslaughter, assault, misconduct in office and reckless endangerment charges. Prosecutors have argued that Porter should be held partially responsible for Gray's death because the officer didn't buckle the man into a seatbelt when checking on him in the back of the transport wagon, and for failing to call for a medic when Gray indicated he needed medical attention. Over the course of the state's case prosecutors sought to emphasize a few key points:

PORTER KNEW THE RULES AND IGNORED THEM

Prosecutors called five witnesses to testify about general orders requiring officers to belt in their prisoners and immediately seek medical care if a detainee appears injured or requests aid. Officer Alice Carson-Johnson, the state's first witness, testified that Porter was a student in her training academy course, and that she taught all recruits to seek aid for any prisoner that requests medical care. "If you recognize that someone is in need of medical assistance, always call for 911 or emergency medical services," she said. Baltimore Police Capt. Martin Bartness, chief of staff to the police commissioner, testified that six updated policies were emailed to all officers just days before the arrest of Freddie Gray, including a policy requiring officers to buckle all detainees in seat belts and to obtain medical care for them "when necessary or requested." Another witness, Andrew Jaffee, an IT specialist for the police department, told jurors that the policies were delivered to Porter's inbox.

'I CAN'T BREATHE'

A central argument in the state's case is that Porter didn't call an ambulance after Freddie Gray told him, 'I can't breathe.' The defense denies that Gray ever uttered those words, however Det. Syreeta Teel, an investigator with internal affairs, testified that she called Porter days after Gray's injury to ask what had happened. At the time Porter was a witness, not a suspect. Teel had previously testified that Porter, during a phone call three days after Gray was injured, told her that during the van's fourth stop, Gray complained to the officer that he couldn't breathe. But in a later recorded statement, Porter says at that time Gray only asked him for help off the van floor, and said yes when Porter asked if the man needed a medic. Referencing the phone conversation, which was not tape recorded, is the only attempt prosecutors made to substantiate the claim that Gray told Porter he couldn't breathe.

PORTER COULD HAVE SAVED GRAY'S LIFE

Several witnesses testified to the extent and nature of Gray's injuries. Dr. Carol Allan, the assistant medical examiner who conducted Gray's autopsy, took the witness stand and testified that Gray was injured by the time Porter met the transport wagon at the van's fourth stop. Allan testified that Gray's injuries, which included a pinch to his spinal cord so severe that it was nearly bisected, occurred between the van's second and fourth stop. Because Porter did not call for an ambulance immediately, instead only requesting that Caesar Goodson, the wagon driver, take Gray to the hospital, the injury worsened to the point of being critical. Dr. Morris Soriano, an Illinois-based neuroscientist, told jurors that if "paramedics had gotten there right away...he would not have suffered the brain injury, which is ultimately what killed him."

PORTER SHOULD HAVE CALLED A MEDIC:

In his statement to investigators Porter said he didn't call for an ambulance after Gray said he needed aid because medics don't come when officers are in possession of their own transport vans. "Medics don't really want to transport our prisoners for us if we have a vehicle," Porter told detectives. But state's witness Angelique Herbert, a Baltimore Fire Department paramedic who treated Freddie Gray, told jurors that in her 17 years on the job she's never once refused a police call for an ambulance.

PORTER SHOULD HAVE BELTED GRAY IN:

The state's final witness, Michael Lyman, a professor of criminal justice at Columbia College, told jurors that officers are required to seek medical attention for their prisoners, whether that means transporting them to the hospital immediately or calling for an ambulance. Additionally, Lyman said there is no reason, barring the officer feeling that he or she is in danger, not to secure a detainee in a seat belt. The responsibility of belting a prisoner, Lyman said, extends across all officers involved in his or her arrest and transport.

The defense will begin its case Wednesday morning.