Image copyright AFP Image caption Freddie Gray's death sparked a national debate

All charges against the last Baltimore police officers facing trial over the death of black detainee Freddie Gray have been dropped.

Mr Gray, 25, died in April 2015 a week after sustaining a spinal injury while in the back of a police van.

Garrett Miller, William Porter and Alicia White were due to face charges including assault, misconduct in office and reckless endangerment.

The move means there will be no convictions in the case.

Prosecutors dropped the charges after earlier trials of three other police officers had ended in acquittals. They announced the move at a pre-trial hearing for Mr Miller on Wednesday.

But speaking afterwards, State Attorney Marilyn Mosby defended her decision to prosecute, saying she stood by her belief that Mr Gray's death was a homicide. "We do not believe that Freddie Gray killed himself," she said.

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A post-mortem report found that Mr Gray sustained his injury by slamming into a van wall during the ride. He was handcuffed but not restrained with a seatbelt.

His death sparked civil unrest in Baltimore, and became part of a wider national debate on police brutality and the death of unarmed black men at the hands of police.

The six officers

Image copyright AFP Image caption Top L-R: Caesar Goodson Jr; Garrett Miller; Edward Nero. Bottom L-R: William Porter; Brian Rice; Alicia White

Brian Rice, aged 41: Mr Rice was one of the three officers who first encountered Gray while on a bicycle patrol and participated in the initial arrest. He was charged with involuntary manslaughter, second degree assault and misconduct in office, among other charges. His trial began on 7 July but he was found not guilty on all counts on 18 July.

Edward Nero, 29: Another one of the three bicycle patrol officers who first encountered Gray. Mr Nero was charged with second degree assault, misconduct in office and reckless endangerment. He went to trial but was found not guilty on all counts in May.

Garrett Miller, 26: The third of the three officers who first encountered Gray. Mr Miller was charged with second degree assault, misconduct in office and reckless endangerment. His trial was due to begin on 27 July but all charges against him were dropped the same day.

William Porter, 25: Became involved after the initial arrest. Prosecutors said Mr Porter was asked twice by Gray for medical assistance but failed to summon any. Mr Porter was charged with involuntary manslaughter, second degree assault, misconduct in office and reckless endangerment. After his first trial ended in a mistrial in December, he was put on trial again last month but the charges were dropped.

Alicia White, 30: Ms White was accused by the prosecution of failing to call for medical assistance for Gray when he was in obvious distress. She was charged with involuntary manslaughter, second degree assault and misconduct in office. Her trial was due to begin in October but all charges against her have been dropped.

Caesar Goodson Jr, 45: Mr Goodson was the driver of the van in which Gray was held. He was charged with second-degree "depraved-heart" murder and manslaughter by vehicle, among other charges. He went on trial in June but was found not guilty on all charges.

Prosecutors had said Mr Miller illegally arrested Freddie Gray after he ran away from a bike patrol officer and was criminally negligent for failing to buckle him into a seatbelt or call a medic when he indicated he wanted to go to a hospital.

Mr Miller, who had testified against colleagues in previous trials, was due to stand trial first, while Mr Porter was to face a retrial in September and Ms White a trial in October.

Series of acquittals

Earlier this month, Lieutenant Brian Rice was cleared by Judge Barry Williams of involuntary manslaughter, reckless endangerment and misconduct in office.

"A mere error in judgment is not enough to show corruption," Judge Williams said in a statement.

Image copyright Murphy, Falcon & Murphy Image caption Freddie Gray died a week after he was arrested

Image copyright Andrew Burton/Getty Images Image caption Freddie Gray's death in April 2015 sparked mass protests throughout Baltimore

In June, officer Caesar Goodson - who drove the van in which Mr Gray rode before he died - was cleared on a second-degree "depraved heart" murder charge, the most serious charge sought against the six officers.

Prosecutors had argued Mr Goodson intentionally gave Mr Gray a "rough ride" while transporting him to the police station but Judge Williams said they had not proved that he "failed corruptly" in his job rather than just making a mistake.

In May, Judge Williams also cleared Edward Nero of second-degree assault, reckless endangerment and two counts of misconduct in office.

Last year a jury failed to reach a verdict in the case of Mr Porter. During his trial, prosecutors said he ignored Mr Gray's pleas for medical help and described the van as a "coffin on wheels".