WASHINGTON — The Justice Department plans to open a wide-ranging civil rights investigation into the practices of the Ferguson, Missouri, Police Department following the shooting last month of an unarmed black 18-year-old by a white police officer in the St. Louis suburb, a person briefed on the matter said Wednesday night.

The person said the investigation could be announced as early as Thursday afternoon. Missouri officials were notified Wednesday of the probe.

The investigation will look at the practices in the past few years of the police department, including patterns of stops, arrests and use-of-force, as well as the training the officers receive, the person said.

The inquiry is separate from an ongoing civil rights investigation the Justice Department is conducting into the shooting of 18-year-old Michael Brown by Officer Darren Wilson on Aug. 9. A local grand jury is also investigating the shooting, which set off about two weeks of unrest in the streets of Ferguson and became a flashpoint in the national discussion of police treatment of minorities across the country. Attorney General Eric Holder two weeks ago visited the St. Louis suburb, where he met with investigators and Brown’s parents and shared personal experiences of having himself been mistreated by the police.

The person spoke on condition of anonymity because the investigation, first reported by The Washington Post, had not yet been announced.