DENVER — The American Civil Liberties Union sued the police department on June 14 for records of internal investigations prompted by complaints the agency kept files on peaceful protesters.

ACLU legal director Mark Silverstein said Police Chief Gerald Whitman denied an open-records request for the documents on grounds that their release would be "contrary to the public interest."

Silverstein says the police department "has it backwards."

"Sunlight is good, and disclosure furthers the public interest," he said.

The city attorney's office said disclosure could violate the "privacy interests" of police officers involved, and said a 2004 court order and a city ordinance prohibits release of such information. Assistant City Attorney Richard Stubbs said in a June 10 letter to the attorney representing ACLU in the case that internal police investigations depend on cooperation from officers and others.

"Disclosure of the files sought could have a chilling effect on the department's ability to obtain that information," Stubbs wrote. "In turn, the department's ability to properly discipline its employees could be damaged."

Silverstein said the courts had overruled the police five times since 1996 and ordered them to release records.

In 2003, the city settled an ACLU lawsuit over the police department's decades-long practice of keeping "spy files" on peaceful protesters. The city agreed to collect information on protesters only if police had reason to suspect criminal activity.

The settlement did not resolve a complaint filed in 2002 by Stephen and Vicki Nash, who are members of a group that monitors police. The Nashes said the spy files labeled them as "criminal extremists," and they asked for an internal investigation and discipline of the officers responsible.

Silverstein said Whitman told the Nashes in March 2004 that there was evidence that department regulations had been violated and that policy changes had been made, but provided no other details. The open-records request — and this week's lawsuit — sought records of those investigations.