BALTIMORE, Dec. 15 (UPI) -- A judge declared a mistrial Wednesday in the prosecution of Baltimore police Officer William G. Porter, the first defendant tried for the death of Freddie Gray, after jurors weren't able to reach a unanimous verdict after 16 hours of deliberations.
Jurors began deliberations Monday after a two-week trial to prove Porter was criminally responsible by his inaction during Gray's arrest. The panel heard from more than 20 witnesses, saw more than 100 exhibits of evidence and heard from medical experts on both sides of the case.
Late Tuesday, jurors told Judge Barry Williams they were deadlocked but were ordered back to deliberations. On Wednesday, Williams declared the mistrial.
It wasn't immediately clear what elements of the case jurors couldn't agree on, but the mistrial means advocates of Gray will be forced to wait until next year before they receive a definitive legal conclusion in the case.
Prosecutors said Porter should have buckled Gray, 25, into the police transport van after his arrest April 12 and radioed for medical help. Investigators said Gray, whose arms and legs were shackled, couldn't brace himself when the van made a sudden movement, fell and hit his head. Gray died April 19 from a spinal cord injury.
Prosecutors argued that Porter's inaction represented criminal negligence. Attorney Janice Bledsoe said Porter had at least four opportunities to help Gray but did not.
"He abused his power," she told the jury in the closing arguments. "He failed in his responsibility. Hold him responsible."
Defense attorneys said the charges are based on conjecture because there is no evidence Porter caused Gray's death. Porter testified that Gray showed no signs of injuries or pain before arriving at the police station. The defense also argued that he should not be held responsible for the death because he never came into contact with Gray during his arrest.
"You're making a legal decision -- not a moral, not a philosophical -- a legal decision," defense attorney Joseph Murtha told the jury. "You set aside the sympathies, you set aside the passions, you look at the cold, hard facts that aren't there in this case."
On Monday afternoon, jurors -- three black men, four black women, three white women and two white men -- began deliberations and immediately asked for the definitions of "evil motive," "bad faith" and "not honestly." They also asked for transcripts of police radio calls and taped interviews with Porter.
Porter is one of six Baltimore officers facing charges in Gray's death and the first to stand trial in the case that became a flashpoint for protests, rioting and race relations nationwide. All six officers involved have pleaded not guilty.
After the jury went out for deliberations, local officials hastened to prepare the community for a possible backlash from the verdict.
Baltimore Mayor Stephanie Rawlings-Blake tweeted she activated the city's Emergency Operations Center "out of an abundance of caution" on Monday. Baltimore police officers were assigned to 12-hour shifts to ensure the department is fully staffed.
Gregory Thornton, CEO of Baltimore City Public Schools, sent a letter to families warning that "student walkouts, vandalism, civil disorder and any form of violence are not acceptable under any circumstances and that students who participate in such behaviors will face consequences."
Baltimore Police Commissioner Kevin Davis urged officers to remain professional, regardless of the outcome of the trial. In a letter to the police force on Monday, he said, "The days ahead present us all an opportunity to show the world why Baltimore is such a special place. Regardless of the outcome of this trial or any future trial, we refuse to surrender to the low expectations of those who wish to see us fail."