Kansas City ? Four members of a Kansas City, Kan., police tactical unit were arrested and released pending formal charges after an internal investigation uncovered evidence of misconduct, the city’s police chief said Wednesday.

Police Chief Rick Armstrong declined to say what the officers are accused of doing because he said he doesn’t want to compromise the investigation. But he said investigators gathered enough evidence Tuesday to warrant arresting the four officers, who are members of the department’s SCORE unit, which is the equivalent to a SWAT team.

“It is with great disappointment that I’m reporting to you today that in the past 24 hours several members of the Kansas City, Kan., police department were arrested during a criminal investigation and released pending the filing of formal criminal charges,” Armstrong said at a news conference. “The officers involved have been placed on unpaid administrative leave.”

Armstrong said he initiated an investigation several months ago after receiving a complaint from outside the department. As the probe developed, he said it became clear the department needed outside help so he brought in the FBI, U.S. attorney’s office and Wyandotte County district attorney’s office.

U.S. Attorney Barry Grissom and Wyandotte County District Attorney Jerome Gorman also spoke at the news conference, and both said it was premature to talk about possible charges because the investigation is still in its early stages.

Armstrong said the department is bracing for a backlash from the community, but called the alleged misconduct an anomaly, pointing out that violent crime dropped dramatically in the city last year because of the work of his officers.

“This is something we have to deal with,” he said. “It’s an embarrassment and we have to expect we’re going to have negative comments as a result of this. However, we have just the most recent year to show a 24-year low in violent crime.”

Earlier Wednesday, Joe Reardon, mayor of the Unified Government of Wyandotte County and Kansas City, Kan., praised Armstrong for launching the probe and pledged his support for the chief’s handling of the case.

“Allegations of misconduct by some members of the KCK Police Department are troubling,” Reardon said in a statement. “As mayor, I expect the utmost integrity and professionalism from our police officers. So do our citizens. Acts of misconduct should not and will not be tolerated.”