The US Justice Department announced Thursday it was opening a civil rights investigation into the Missouri police department involved in the racially charged shooting of an unarmed black teenager.

The death of 18-year-old Michael Brown has already given rise to a separate federal investigation into whether Darren Wilson, the police officer who shot him, violated the teenager’s civil rights.

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But Attorney General Eric Holder told reporters that the Department of Justice had also determined there was cause to investigate “whether Ferguson Police officials have engaged in a pattern or practice of violations of the US Constitution or federal law.”

Brown’s shooting on August 9 and subsequent violent protests reopened a fierce national debate on race and the tactics used by police in dealing with minorities.

Holder, himself an African-American, visited Ferguson amid the protests, walking the streets and talking with community members.

“The decision to go ahead was based not only on what I heard,” Holder said, but also public records and other documents involving minorities.

He added that the investigation “is not a stopgap or a short-term solution” but rather “a long-term strategy” meant to build trust, safety and accountability.

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In addition, a grand jury is hearing evidence to determine whether Wilson, 28, used excessive force in fatally shooting Brown, who was hit at least six times.

Witnesses have given varying reports as to the circumstances surrounding Brown’s death, with some saying the teenager had reached for Wilson’s gun, while others, including a friend who was with Brown, said he had his hands in the air.

Brown’s family responded to the announcement saying it was encouraged, and urged the use of body cameras for police around the country.

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“We can’t have another young man’s life taken amid murky circumstances. We want the truth to shine brightly,” the family’s lawyer, Ben Crump, said.

Ronald Davis, director of the Department of Justice’s Office of Community Oriented Policing Services, said “the recent disturbances in Ferguson have revealed significant mistrust between the community and police agencies throughout the county.”

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Amnesty International meanwhile welcomed the announcement but said “the department should also investigate any human rights abuses in connection with the policing of protests in Ferguson.”

Over the past five years, the Justice Department has conducted similar investigations to the one announced Thursday in 20 police departments and is helping enforce 14 agreements to reform practices across the United States, Holder said.