A top Bronx prosecutor testified that a high volume of baseless trespassing arrests by the NYPD led her to order a crackdown on prosecuting the cases this year as a closely watched Manhattan federal court test of city police stop-and-frisk practices began Monday.

"I said enough is enough," Jeannette Rucker, chief of the Bronx district attorney's complaints bureau, told U.S. District Judge Shira Scheindlin. "We have to stop this."

The New York Civil Liberties Union alleges in the case that police have abused the so-called "Clean Halls" program, in which thousands of private apartment buildings citywide have authorized the NYPD to patrol, by using trespass as an excuse to stop, question and at times arrest tenants or their guests.

The case, which focuses on the Bronx, is the first to go to trial of three suits Scheindlin is overseeing that could reshape the NYPD's controversial stop-and-frisk practices. The judge has certified a class action in a challenge to use of the tactic citywide, and another case challenges the use of trespass charges in public housing.

In testimony Monday, an expert, Jeffrey Fagan of Columbia University, said that he analyzed police reports on 1,857 stops made outside of "Clean Halls" buildings in the Bronx in 2011 in which trespass was cited as the reason, and concluded that the reports articulated no adequate legal justification for 62 percent of them.

Civil liberties union lawyer Christopher Dunn, who wants the judge to issue an injunction against baseless stops, said use of claimed suspicion of trespass to corral people on public sidewalks "illustrates in a concrete way" the broader problems with stop and frisk. He said people targeted by stops will testify later in the case.

"Here, people are walking into and out of their own homes," he told the judge. "These stops are an assault on the sanctity of the home."

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The NYPD says stop and frisk is a critical tactic to control drugs, guns and street crime. City lawyers disputed the NYCLU's statistics, and said new training programs and internal procedures have been adopted to address complaints about "Clean Halls" and broader stop-and-frisk tactics.

"There has been no deliberate indifference on the part of the NYPD or its policy makers," attorney Mark Zuckerman said.