Tens of thousands of times over six years, the police stopped and questioned people on New York City streets without the legal justification for doing so, a new study says.

And in hundreds of thousands of more cases, city officers failed to include essential details on required police forms to show whether the stops were justified, according to the study written by Prof. Jeffrey A. Fagan of Columbia Law School.

The study was conducted on behalf of the Center for Constitutional Rights, which is suing the New York Police Department for what the center says is a widespread pattern of unprovoked and unnecessary stops and racial profiling in the department’s stop-question-and-frisk policy. The department denies the charges.

The study examined police data cataloging the 2.8 million times from 2004 through 2009 that officers stopped people on the streets to question and sometimes frisk them, a crime-fighting strategy the department has put more emphasis on over the years.