The Baltimore Police Department has routinely violated the constitutional rights of residents, according to a US Justice Department investigation stemming from the death of black detainee Freddie Gray last year.

The Justice Department probe, the results of which will be officially released at a news conference in Baltimore on Wednesday morning, was launched shortly after Gray's death in April 2015.

Police had arrested Gray, 25, for fleeing unprovoked in a high-crime area. He suffered a neck injury in a police wagon while shackled and handcuffed, and died a week later.

Gray's death triggered rioting in Baltimore, a majority-black city of about 620,000 people. It fuelled a national debate on police tactics and stoked the rise of the Black Lives Matter movement.

READ MORE: Last charges dropped against police in Freddie Gray case

The Justice Department's 163-page report found that the Baltimore Police Department has routinely made unconstitutional stops, searches and arrests, and these illegal practices have disproportionately affected the city's black residents.

Police have also engaged in a pattern of using excessive force and retaliated against people engaging in constitutionally protected expression, the investigation found.

"This pattern or practice is driven by systemic deficiencies in BPD's policies, training, supervision, and accountability structures that fail to equip officers with the tools they need to police effectively and within the bounds of the federal law," the report said.

A spokesman for the Baltimore Police Department did not immediately respond to a request for comment, the Reuters news agency said.

Six officers were charged over Gray's death, but four trials ended without a conviction. Prosecutors dropped the remaining charges last month.

Source: Reuters