Washington, May 9 (IANS/EFE): The US Department of Justice will investigate the Baltimore City Police Department to determine whether it "has engaged in a pattern or practice of violations of the Constitution or federal law," Attorney General Loretta Lynch said.

The announcement came two days after Baltimore Mayor Stephanie Rawlings-Blake formally requested the probe in the wake of the death in police custody of Freddie Gray, a 25-year-old African-American man.

"Our goal is to work with the community, public officials and law enforcement alike to create a stronger, better Baltimore," Lynch told reporters on Friday.

"(C)ommunities that have gone through this process are experiencing improved policing practices and increased trust between the police and the community," the attorney general added.

Gray died on April 19, a week after suffering a severe spinal injury while being transported to a police station.

His death set off days of protests and parts of Baltimore were rocked by violent disturbances on April 27 following Gray's funeral, prompting authorities to declare a state of emergency and impose a 10 p.m.-5 a.m. curfew.

Residents celebrated late last week when the state's attorney filed charges against the six police officers - three of them black - involved in Gray's death, and authorities subsequently lifted the curfew.

"The challenges we face did not arise in a day, and change will not come overnight. It will take time and sustained effort," Lynch said.

"But the people I met in Baltimore - from protestors to public officials to an officer who had been injured amidst the violence - all said the same thing: 'I love my city and I want to make it better.' That's why I'm so optimistic about this process," she said.

The Freddie Gray case has emerged as the first major test for Lynch since her swearing-in on April 27.

Eric Holder, Lynch's predecessor, ordered an investigation of police in Ferguson, Missouri, following the fatal shooting of unarmed African-American teenager Michael Brown by a white officer last August.

The probe concluded that the overwhelmingly white Ferguson police department did engage in a "pattern or practice" of abusive conduct in a community where 70 percent of the residents are black.

Lynch and Holder are both African-American.

The Baltimore police department has long been criticised for its treatment of the city's mainly black population.

The Sun, Baltimore's newspaper of record, published last year an investigative series detailing instances of police brutality against subjects which included children and the elderly.