William Porter, 26, stands accused of involuntary manslaughter, reckless endangerment and assault in the death of the 25-year-old black man. Porter, himself black, has pleaded not guilty to the charges.

Because of the extensive media coverage the case garnered following Gray's death on April 19, lawyers representing the accused police officers have said finding impartial jurors will be impossible, although Judge Barry Williams went through with the formal selection of jurors anyway.

Lawyers also requested to have the trial moved from Baltimore, where tension is still high following a series of protests that swept parts of the city in response to the case. The judge refused.

Porter is being tried first because prosecutors want him to testify against the other officers.

Unrest in Baltimore

Gray was arrested and charged with possession of a knife. Then he was shackled and loaded into a police van. At some point during the ordeal, he fell into a coma and later died in the hospital from injuries sustained during the van ride.

Riots broke out in Baltimore following Gray's funeral, causing Maryland Governor Larry Hogan to declare a state of emergency in May and send thousands of National Guard troops to the city.

Baltimore paid Gray's family a settlement of $6.4 million (5.7 million euros) in September.

blc/gsw (AP, dpa, AFP)