US Attorney General Eric Holder sought to reassure the people of Ferguson about the inquiry into the shooting death of a black 18-year-old by a white police officer.
He said he understands why many black Americans do not trust police, recalling how he was repeatedly stopped by officers who seemed to target him because of his race.
Mr Holder made the remarks during a visit to the St Louis suburb that has been hit by more than a week of unrest since the August 9 shooting of Michael Brown.
The Obama administration intended the trip to underscore its commitment to civil rights in general and the Ferguson case in particular.
The attorney general remembered how he was stopped twice on a New Jersey highway and accused of speeding. Police searched his car, going through the boot and looking under the seats.
“I remember how humiliating that was and how angry I was and the impact it had on me,” Mr Holder said during a private meeting with about 50 community leaders at St Louis Community College.
He also met officials investigating Mr Brown’s death, the teenager’s parents and Missouri State Highway Patrol Captain Ron Johnson, who has been in charge of security in the community for nearly a week since relieving Ferguson police.
The National Guard has also been called in to help keep the peace.
Asked whether he had confidence in the local investigation of the police officer, Mr Johnson said Mr Holder’s presence “is a guarantee on that”.
In nearby Clayton, a grand jury began hearing evidence to decide whether the officer, Darren Wilson, should be charged over Mr Brown’s death.
A spokesman for St. Louis County Prosecutor Bob McCulloch said there was no timeline for the process, but it could take weeks.
At the college, Mr Holder told his audience the most experienced agents and prosecutors would be assigned to the Ferguson investigation.
The justice department has mounted an unusually swift and aggressive response to Mr Brown’s death, conducting an independent post-mortem and sending dozens of FBI agents to Ferguson in search of witnesses to the shooting.
Mr Holder said the Obama administration has been trying to achieve change through the justice department’s civil rights division.
“The same kid who got stopped on the New Jersey freeway is now the attorney general of the United States,” he added.
“This country is capable of change. But change doesn’t happen by itself.”
Outside the St Louis County Justice Centre in Clayton, where the grand jury convened, two dozen protesters gathered in a circle for a prayer, chanted and held signs urging Mr McCulloch to step aside.
Mr McCulloch’s close family connections to police have been cited by some black leaders who question his ability to be impartial in the case.
His father, mother, brother, uncle and cousin all worked for the St Louis Police Department, and his father was killed while responding to a call involving a black suspect.
The prosecutor, who is white, has insisted his background will have no bearing on the handling of the Brown case, which has touched off a series of night-time protests during which authorities used tear gas and rubber bullets to clear the streets.
The protests were more subdued on Tuesday night, with smaller crowds, fewer confrontations and no tear gas.
Police said they still made 47 arrests, mainly of people who defied orders to disperse.
Tensions rose briefly when someone hurled a bottle at officers, but there were no reports of gunfire or the type of clashes that had marked previous nights.
Yesterday, police said an officer had been suspended for pointing a semi-automatic assault rifle at demonstrators, then swearing and threatening to kill one of them.
A protester captured the exchange on video and posted it on YouTube and other websites.