William Porter’s trial was the first test of prosecutors’ case against six officers in a city struggling to rein in violent crime. The case hinged not on what Porter did, but what prosecutors said he didn’t do. He was accused of failing to get medical help for a critically wounded Gray and was charged with manslaughter, assault, misconduct in office and reckless endangerment.

The charges carried maximum prison terms totalling 25 years. It was not immediately clear whether Porter would be tried again.

Wednesday was the third day of deliberations for the jury of seven women and five men. They deliberated for a total of about 15 hours. On Tuesday, they indicated they were deadlocked, but the judge told them to keep working.

Meanwhile, during deliberations on Wednesday, a handful of protesters gathered outside the courthouse, chanting “send those killer cops to jail”.

Gray, who was arrested while fleeing from police, died on April 19, a week after his neck was broken while the seven-block trip turned into a 45-minute journey around West Baltimore. The autopsy concluded that Gray probably suffered the injury from being slammed against the compartment’s metal wall during cornering or braking.

Gray was black. Porter is also black, as are two of the other five officers charged.

It wasn’t clear how the mistrial would affect the State’s cases against the other officers. Prosecutors had planned to use Porter’s testimony against two of his fellow officers.