CHICAGO (AP) — Chicago Police say they made dozens of arrests after infiltrating an invitation-only group on Facebook where they bought purchased guns and drugs.

But in announcing the nearly-year-long operation on Thursday, Police Superintendent Eddie Johnson harshly criticized Facebook for what he said was the websites unwillingness to help officers at all. Facebook did not immediately respond to an email from The Associated Press seeking comment.

Police say the investigation started when an informant told the department’s narcotics division about the Facebook group that couldn’t be found through the search function. Once investigators infiltrated the group — an effort that took months, police say, because of Facebook’s unwillingness to help —they seized 18 guns and $46,000 worth of drugs. Then they arrested 50 people and secured arrest warrants for 18 more.