By Shimon Prokupecz, Pamela Brown and Greg Botelho
(CNN) -- The U.S. Justice Department is planning to take a top-to-bottom look at the Ferguson, Missouri, police department, which has come under fire for its past practices in the uproar over the shooting of Michael Brown, officials told CNN.
A Missouri official and a federal official told CNN on Wednesday that the civil rights division of the Justice Department is preparing to launch a new investigation into police in the St. Louis suburb. Attorney General Eric Holder could make an announcement about the investigation as early as Thursday, an official briefed on the investigation said.
The review will examine previous incidents and complaints involving police, as well as its training, to examine how the department operates, according to the Missouri official. It will look at whether the practices of Ferguson police -- and only Ferguson police -- violate federal law or the U.S. Constitution, said an official briefed on the investigation.
Such probes typically focus on paving the way for systemic reform going forward, rather than punishing misconduct from the past, said CNN senior legal analyst Jeffrey Toobin. Nonetheless, they can produce significant changes within a department.
"It's very serious," Toobin said of the expected investigation, "because it can lead to a virtual federal takeover of the police, as happened recently in New Orleans."
Justice Department representatives met with Ferguson officials in Missouri and informed them of the intent to launch the preliminary probe, said the Missouri official, who had direct knowledge of the meeting.
It is distinct from the Justice Department's previously announced civil rights probe that is specific to the August 9 shooting of Brown, an unarmed African-American teenager, by Ferguson police Officer Darren Wilson, who is white. Proving a civil rights violation would require showing that Wilson was actively hostile to Brown because of his race.
The shooting and the fact authorities didn't immediately, and still haven't, charged Wilson spurred emotional and, at times, violent protests on the streets of Ferguson.
Dozens were arrested over those tense few weeks, which were sometimes marred by looting and clashes between protesters and law enforcement.
Brown's shooting also stirred up locals' gripes about Ferguson police over the years. Some of them said members of the predominantly white police force would routinely and inordinately single out African-Americans, who make up two-thirds of the St. Louis suburb's population.
Many African-Americans said that they often found themselves subject to racial profiling -- such as being pulled over for no obvious reason besides, they presumed, "DWB," or driving while black.
Some white residents complained police have acted in a heavy-handed fashion.
Chief Tom Jackson has said the claim that officers are more likely to stop blacks is more perception than reality.
Other cases, though, went well beyond that.
The family of Jason Moore recently filed a lawsuit accusing police of excessive force, saying he died of cardiac arrest on September 17, 2011, after police fired Tasers at him.
The family says that Moore, who they say suffered a psychological disorder, was walking around naked and posed no threat to police.
It's not clear which cases, specifically, the new federal investigation will examine. The probe will not focus on law enforcement's response to Brown-related protests, since that effort involved numerous agencies and Ferguson did not lead this multi-agency effort.
Ferguson will be the latest of many local police and sheriff departments nationwide to be subject to such a federal investigation, which Toobin explains are launched "when there are persistent allegations of misconduct."
This April, for instance, the Justice Department lambasted police in Albuquerque, New Mexico, for what it characterized as a longstanding history of police brutality and unnecessary deadly force, sometimes "in an unconstitutional manner." The report laid out several measures to address the problems, such as changing policies, training procedures and recruitment protocol.
Police departments in Los Angeles, Pittsburgh, Cincinnati and elsewhere have agreed to Justice Department plans to address controversial policies and patterns of alleged misconduct.
But nowhere has the federal agency come down harder than on the New Orleans police department, which has been plagued for years by allegations of corruption, excessive use of force, illegal searches and widespread racial discrimination.
In July 2012, Holder detailed a consent decree -- which he called the most wide-ranging such agreement in U.S. history -- that includes more than 100 recommendations dealing with virtually every aspect of the department.
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