IF THERE were any doubt that the citizens of Ferguson, Mo., had good reason to question the professionalism of their police force, it has been erased by several days of revelations about the shooting of teenager Michael Brown.

The facts we now have include these: Ferguson Police Officer Darren Wilson killed the 18-year-old Mr. Brown when he was unarmed and more than 30 feet from the police car in which an initial confrontation between the two apparently occurred. On Monday, the public got some bits of new information, including autopsy reports indicating that Mr. Brown was shot from the front and that the teenager had marijuana in his system. A secondhand account of Officer Wilson’s side of the story also emerged. But these bottom-line points stand: Police officers have a responsibility to use non-deadly means to defuse situations whenever possible, and nothing on the record indicates that Mr. Brown had to die.

Meanwhile, the Ferguson Police Department continues to fumble the vital job of providing information to the public about the shooting. When local officials have produced information, its release has often been self-servingly selective. Authorities waited days even to identify Officer Wilson. Crucial details of the shooting remain murky — including the officer’s full, on-the-record account of the story — yet Ferguson police released extensive documentation of a convenience store robbery in which Mr. Brown was allegedly involved. If the intent of the police is to avoid prejudicing eyewitness accounts still being collected, this is an awful way of doing so. Instead, this looks like contempt for the public’s right to know, incompetence or both.

There was a moment at which tensions seemed to be cooling. After days of clashes between protesters and police toting military-style weapons, Missouri Gov. Jay Nixon (D) relieved the St. Louis County Police Department of the job of securing Ferguson. The Missouri Highway Patrol commander the governor tapped to step in made a concerted effort to engage with the community. Nighttime unrest briefly abated. Then the robbery information and the contradictory explanations for its release helped bring the situation back to a boil.

Police misbehavior is no excuse for violence and looting. But in such a powder-keg situation, a key role for the government is to calm rather than to inflame. The Ferguson police failed that basic test.

It is good that federal authorities are conducting a thorough parallel investigation and that President Obama will dispatch Attorney General Eric H. Holder Jr. to Ferguson this week. Federal officials should conduct their probe as quickly as possible and release as much information as they can, as soon as they can. Not only would that show more respect for the people of Ferguson than their own police have; it would apply pressure to local authorities to conduct themselves more responsibly.