The US Department of Justice told the court, in a surprise last-minute filing, that it would prefer an independent monitor to help ensure changes, should the city of New York lose this case.

The government filed its “statement of interest,” however, somewhat reluctantly. It would have preferred to weigh in “if, and only if,” the statement said, the court had already found the NYPD’s tactics violate the Constitution. But the judge in the case, Shira Scheindlin, had consolidated the so-called liability and remedy phases of the trial, requiring all interested parties to submit their briefs before she makes her decision, expected this summer.

The Justice Department (DOJ) offered no opinion on the constitutionality of this crime-fighting tactic, which allows any New York City police officer to stop, question, and frisk a person for weapons if the officer reasonably suspects that person is engaged in a criminal activity. But it did zero in on the most contentious of the remedies sought by the private citizens who brought the class-action lawsuit: the appointment of an independent monitor to oversee changes in the NYPD.

Mayor Michael Bloomberg and Police Commissioner Raymond Kelly have each bristled at the suggestion of an independent monitor throughout the course of the 2-1/2-month trial, which ended in May. They cite the "stop and frisk" policy as instrumental in driving down the city's crime rate.

“We think that a monitor would be even more disruptive than an IG,” responded Mayor Bloomberg on Thursday, also referring to a separate City Council proposal to appoint an inspector general for the NYPD. “It just makes no sense whatsoever, when lives are on the line, to try to change the rules and hamper the police department from doing their job.... They comply with the law. We are 100 percent confident in that,” he said Thursday at a press conference in Queens.

But the trial did not go well for the city, some observers believe. The Justice Department’s last-minute filing may indicate that it, too, feels it must weigh in at this late stage because the city will probably lose the case.

“The whole thing is unusual,” says Randolph McLaughlin, a New York-based civil rights attorney and a Pace Law School professor who has represented plaintiffs in police misconduct cases for more than 15 years. “I mean, if the DOJ doesn’t feel there’s a likelihood that the case will go for the plaintiffs, then why get involved? Why alienate the city of New York and the NYPD?

“I would have to believe, knowing some of the lawyers who practice in the US Attorney’s office, that they’ve been monitoring this case closely, and I do think they’re reading the same tea leaves I’m reading, and they believe or have a feeling or suspicion that the case is not going well for the city,” Mr. McLaughlin says.

In a few other major US cities – such as Los Angeles, Philadelphia, and Boston – police have used the stop and frisk tactic, but none has seen the controversy surrounding it that has embroiled New York.

Earlier this year, Judge Scheindlin found that an element of the NYPD’s stop-and-frisk tactic violated the Fourth Amendment’s protection against unreasonable search and seizure. Police had been routinely stopping people outside private apartment buildings in the Bronx, under the suspicion they were trespassing. In this case, she wrote in her finding for the plaintiffs, the evidence “strengthens the conclusion that the NYPD’s inaccurate training has taught officers the following lesson: Stop and question first, develop reasonable suspicion later.”

Scheindlin will also be ruling on whether the NYPD’s stop-and-frisk tactics illegally target minorities. In 2012, police made 533,042 stops under the program, and roughly 87 percent were of blacks or Hispanics. In the vast majority of these stops – about 9 in 10 – those stopped walked away without being arrested or even ticketed.

If she again finds these tactics unconstitutional – and she continues to seem skeptical of crucial parts of the city’s defense – she could order another injunction, or order specific changes to the tactics, or even consider other remedies, such as equipping officers with body-worn cameras, a possibility she found intriguing during the trial.

Despite its reluctance to get involved in the question of the constitutionality of "stop and frisk," the Justice Department says it strongly favors an independent monitor.

“The implementation of an injunction to address structural deficiencies in a law enforcement agency where those deficiencies contribute to a pattern of constitutional violations is a complex and difficult task,” the statement argued. “A monitor provides the independence and expertise necessary to conduct the objective, credible analysis upon which a court can rely to determine whether its order is being implemented, and that gives the parties and the community confidence in the reform process.”