IN PRINCE George’s County, it is now clear that the police, without provocation, can beat an unarmed young student senseless — with impunity. They can blatantly lie about it — with impunity. They can stonewall and cover it up for months — with impunity. They can express no remorse and offer no apology — with impunity.

The agent of this travesty of justice, and this impunity, is Judge Beverly J. Woodard of the Prince George’s County Circuit Court. Judge Woodard has presided in the case involving John J. McKenna, a young University of Maryland student who was savagely beaten by two baton-wielding Prince George’s cops in March 2010, following a men’s basketball game on the College Park campus.

The beating of Mr. McKenna was videotaped; had it not been, the police, who filed no report and then falsely claimed that he instigated the incident and attacked them, may never have been investigated or charged. Yet despite the fact that a jury convicted one of the police officers, James Harrison Jr., of assault nearly two years ago, Judge Woodard has now thrown the verdict out and closed the case.

The judge offered no explanation for her actions, and no wonder. What possible explanation could there be for exonerating Mr. Harrison? Mr. McKenna, now a law student at Catholic University, was simply skipping down the street when he rounded a corner and encountered police on horseback. As he started to back away, clearly meaning no harm, two officers on foot rushed him and beat him senseless with their batons. Mr. Harrison’s blows were particularly vicious.

There were dozens of witnesses, including police. Yet what followed was an official wall of silence, dishonesty and denial from the department. Mr. McKenna’s injuries, the police initially said, were sustained when he was kicked by a horse.

The cops’ story fell apart when the video surfaced, but even then their stonewalling continued. For months, no one would identify the officers in riot gear who were shown beating Mr. McKenna.

It was only due to the persistence of Mr. McKenna’s lawyers that the cover-up and lies were shredded. At trial, in late 2012, a jury convicted Mr. Harrison on a felony charge of assault. Another officer, Reginald Baker, was acquitted, although he, too, used his baton to beat Mr. McKenna as he lay stunned and defenseless on the ground.

Judge Woodard conducted herself unprofessionally at trial. She failed to disclose an apparent conflict of interest — she had been previously married to a Prince George’s officer who himself was convicted for brutality — until asked about it by a journalist. In court, she exhibited what many observers regarded as overt hostility toward Mr. McKenna, the victim.

In Maryland, judges sometimes toss out convictions for first-time offenders in minor cases. This is another matter — a clear case of egregious police brutality. Mr. Harrison, who was allowed to retire from the department with a full pension, may now work again as a police officer if he wishes.

In a separate proceeding, the county was forced to pay $2 million to Mr. McKenna to settle a civil lawsuit arising from the beating. That’s fine. But for Mr. Harrison to walk away scot-free from his conduct, for which he has still not apologized or expressed remorse, is a disservice to the public. The message it sends to the county police — that they will suffer no consequences for blatant and violent misconduct — is dangerous.