After listening to two months of testimony on the New York Police Department’s stop-and-frisk practices, Judge Shira A. Scheindlin left little doubt about her views of their effectiveness in helping detect criminal behavior.

“A lot of people are being frisked or searched on suspicion of having a gun and nobody has a gun,” Judge Scheindlin, of Federal District Court in Manhattan, said on Monday during closing arguments in the trial. “So the point is: the suspicion turns out to be wrong in most of the cases.”

Judge Scheindlin’s remarks punctuated more than five hours of summations, as civil rights lawyers and those representing the city offered dueling interpretations of many weeks of testimony from scores of witnesses. And her remarks were far more critical and blunt than those she had previously made during the trial.

Observing that only about 12 percent of police stops resulted in an arrest or summons, Judge Scheindlin, who is hearing the case without a jury, focused her remarks on Monday on the other 88 percent of stops, in which the police did not find evidence of criminality after a stop. She characterized that as “a high error rate” and remarked to a lawyer representing the city, “You reasonably suspect something and you’re wrong 90 percent of the time.”