Baltimore police officer Caesar Goodson Jr. was found not guilty on Thursday of all charges in the death of black detainee Freddie Gray, including the most serious charge of second-degree "depraved heart" murder.

Judge Barry Williams handed down the verdict in Baltimore City Circuit Court. Goodson, 46, was the driver of a police transport van in which Gray broke his neck in April 2015

Goodson also faced three counts of manslaughter, reckless endangerment, second-degree assault and misconduct in office.

Freddie Gray, 25, was arrested for possessing a switchblade knife outside a housing project on Baltimore's west side. According to his attorney, Gray died a week later in the hospital from a severe spinal cord injury he received while in police custody. (Family photo/Murphy, Falcon & Murphy) (Murphy, Falcon & Murphy)

"Depraved-heart" second-degree murder is a charge that can result in Maryland and other states when the suspect is believed to have had a reckless disregard for another person's life.

Gray's death led to protests and riots and galvanized many — including the Black Lives Matter movement — who said the city's government has long ignored their pressing needs.

Prosecutors contended Goodson gave Gray a "rough ride," failed to ensure his safety and should have called for a medic.

Goodson's defence team argued that Gray caused his own injuries by falling inside the transport van. Goodson also lacked the training to recognize that Gray was hurt, they said.

Goodson, who is also black, faced the most serious charges among the six officers charged in Gray's death, making his the marquee case for prosecutors. They failed to secure a conviction in two earlier trials of officers.

Goodson waived a jury trial, leaving it to Williams to decide his fate.

Officials and residents reacted to the acquittal of the police van driver.

State Senator Catherine Pugh, the Democratic nominee in Baltimore's mayoral race, issued a statement Thursday after the judge gave his verdict. She urged residents to be patient.

"Protests are a vital part of democracy, but to destroy the homes and businesses many people have worked very hard to build is unacceptable.… It is important to respect each other and to respect our neighbourhoods."

Gray's death last year set off protests and violence at the time.

Republican Gov. Larry Hogan's office also issued a statement. It said he respects the legal process and verdict, noting that "over the past year, the people of Baltimore city have made tremendous progress in rebuilding their communities and businesses."

Outside the courthouse, a small group of protesters chanted before the verdict: "We can't stop. We won't stop, till killer cops are in cell blocks."