Jurors have begun deliberating whether a Baltimore police officer is guilty of manslaughter and assault in the death of Freddie Gray, a black man who died from a spinal cord injury sustained in police custody last April.

The deliberations started early Monday afternoon following prosecution and defense closing arguments.

William Porter, who also is black, is the first of six police officers to be tried in connection with Gray's death. The incident sparked protests in Baltimore and raised questions about police negligence.

Police had not secured Gray with a seat belt in the police van, which the defense has said is not unusual in Baltimore. The Baltimore Sun reported that prosecutor Janice Bledsoe "began an impassioned closing argument by holding up a seat belt and clicking it. 'That's all it would've taken,' Bledsoe told jurors."

NPR's Jennifer Ludden, reporting from Baltimore, told our Newscast unit that prosecutors pointed out inconsistencies in Porter's testimony:

"They said Porter showed callous indifference when he failed to seat-belt Gray in a van, or call a medic when Gray said he wanted one. Criticizing a key defense argument, prosecutors said the fact officers often do not seat-belt detainees is no excuse."

Porter's defense attorney Joseph Murtha asserted that there wasn't enough evidence to convict, NPR reported.

"Defense attorney Joe Murtha attacked the state medical examiner as unreliable. He said her autopsy still does not explain exactly what happened to Gray in the police van. He told jurors — the state wants you to reach a conclusion based on 'speculation and conjecture.' "

Ludden has reported that the key question in the case against Porter is when Gray sustained the injury that caused his death:

"After two weeks of testimony, that is a mystery we still do not know. Both sides agreed that somehow while Gray was handcuffed and shackled and not seat-belted, he managed to stand up and was kind of thrown forward by the van's movement."Now, [a] Maryland assistant medical examiner and another prosecution expert believe this happened before Officer William Porter checked on Gray. This would be at the fourth and fifth stops of this police van. And they say at that point, Gray would have been losing his ability to move limbs, breathe and talk. And they say Porter should have realized he was injured and should have called a medic when Gray said he wanted one. ... Forensic experts called by the defense have argued that Gray did not fall until near the end of this van ride and that he was instantly paralyzed shortly before he was found unconscious. And so that scenario would basically let Porter off the hook a bit."

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