WASHINGTON (Reuters) - A privacy group sued the New York Police Department on Tuesday to demand the release of documents related to its use of facial-recognition technology, which rights groups have criticized as discriminatory and lacking in proper oversight.

The lawsuit is the latest attempt to compel U.S. law enforcement agencies to disclose more about how they rely on searchable facial-recognition databases in criminal investigations.

NYPD has previously produced one document in response to a January 2016 freedom of information request, despite evidence it has frequently used an advanced face-recognition system for more than five years, according to the Center for Privacy & Technology at Georgetown University law school, which filed the suit in New York state court.

“The department’s claim that it cannot find any records

about its use of the technology is deeply troubling,” said David Vladeck, the privacy group’s faculty director. He added that an absence of responsive documents, such as contract and purchasing documents, training materials or audits, would be an indication the police force did not possess controls governing its use of facial-recognition software.

NYPD could not be immediately reached for comment on the suit.

Facial-recognition databases are used by police to help identify possible criminal suspects. They typically work by conducting searches of vast troves of known images, such as mug shots, and algorithmically comparing them with other images, such as those taken form a store’s surveillance cameras, that capture an unidentified person believed to be committing a crime.

But the technology has come under increased scrutiny in recent years amid fears that it may lack accuracy, lead to false positives and perpetuate racial bias. [nL1N1CO1A0]

Democratic and Republican lawmakers expressed consternation at the secrecy surrounding facial-recognition technology during a U.S. House Oversight Committee hearing in March.

The Center for Privacy & Technology released a report last year concluding half of America’s adults have their images stored in at least one searchable facial-recognition database used by local, state and federal authorities.

The study, titled “Perpetual Line-Up,” found that states rely on mug shots, driver’s license photos, or both in assembling their databases, and that images are often shared with the Federal Bureau of Investigation.

The U.S. Government Accountability Office estimated last year that more than 400 million facial pictures of Americans were stored in databases kept by law enforcement agencies.