NYTimes

The two men appeared in quick succession, a police lineup turned on its head. The men were police officers, ordered to a courtroom on Monday so a witness could identify them as the officers who had stopped and frisked him.

The unusual scene underscored an emerging theme in the stop-and-frisk trial under way in Federal District Court in Manhattan: for those stopped and frisked, the experience is an ordeal they will long remember. But for the officers, it can be a nonevent, as their inability to recall these encounters shows.

Over the last month, a number of officers called to the stand have struggled to remember the precise details of street encounters that happened as long as five years ago. Indeed, forgetfulness has taunted the trial at nearly every turn, frustrating efforts to determine what really happened during many of the police stops that are the foundation of a case examining the constitutionality of the Police Department’s tactics.

On Monday, forgetfulness itself was at issue. Judge Shira A. Scheindlin ordered the two officers, Sgt. James Mahoney and Detective Scott Giacona, back to court. The officers were accused of stopping a witness, Leroy Downs, on Staten Island in 2008, but they had previously claimed under oath that they had no recollection of stopping him.

On Friday, the judge raised the possibility of a perjury prosecution stemming from the Downs stop. “Somebody may not be testifying completely accurately under oath, and I’m troubled,” she said.

Andrew Quinn, the lawyer for Sergeant Mahoney, responded that ordering the officers into the courtroom for the purposes of being identified by Mr. Downs would be “blatantly suggestive” that they were in fact the ones who stopped him. “If the police tried to do this, Judge,” Mr. Quinn added, but the judge interrupted, saying that police eyewitness identification procedures did not apply to her.

“I’m not bound to any rules of lineup, show-ups, or anything else,” Judge Scheindlin said, noting this was not a criminal trial. “I want the man to see these two people up or down, yes or no. That’s the end of it.”

So on Monday, the officers and Mr. Downs took the stand in quick succession: Sergeant Mahoney and Detective Giacona said they did not recognize Mr. Downs.

Mr. Downs, however, had no such difficulty, recalling the officers as the men who had stopped him on Staten Island.

Mr. Quinn told reporters there was no reason for officers to recall each stop from years ago. “No more than you would remember what you ate for breakfast five years ago,” he said.

At times, officers have tripped over crucial details, and lawyers for the city have tried to suggest that time, rather than credibility, was at issue. One officer, Edward Arias, testified that he had stopped a man partly on the basis of the coat he was wearing: it fit the description of a suspect wanted in an unsolved robbery pattern. “I remember distinctly that the pattern mentioned a beige, yellowish, beige coat,” he testified.

But the officer was confronted with a statement he gave several years ago in which he said he had been searching for a suspect wearing a blue coat, not a yellowish one.

At times, the stops have been hazy to even Judge Scheindlin, hearing the case for more than a month now. While listening to an officer describe a stop, the judge asked the lawyers if the court had already heard testimony from the man who had been stopped.

Yes, the judge was told, as lawyers gave details of his testimony: one stop occurred outside a Chinese restaurant, another on the subway platform. “I don’t remember too much about it,” the judge said. “It was a whole week ago.”