CHICAGO – A federal judge this week dismissed Cook County, Ill., Sheriff Tom Dart’s lawsuit attempting to force online classified ads site Craigslist to close its “adult services” section.The lawsuit, filed in March, alleged the website facilitates prostitution and other sex crimes. In a prepared statement released at the time, Dart called Craigslist the “single largest source of prostitution in the nation” and stated “Craigslist unabashedly facilitates prostitution, then ultimately makes a profit from it.” According to documents filed in Dart’s case, Craigslist has made about $80 million in revenues so far this year, much of it generated by ads that caused Dart’s department and others nationwide to spend a disproportionate amount of dollars and manpower on enforcing local laws.

In dismissing the suit, U.S. District Judge John F. Grady ruled the Craigslist ads don’t offer sex explicitly. In addition, he noted, the federal Communications Decency Act immunizes “intermediary” online services like Craigslist from charges of facilitating illegal activities.

In his suit, Dart claimed hookers, pimps and other sex traffickers use Craigslist to hawk their wares, and that by hosting the ads and allowing advertisers to include contact details, Craigslist tacitly “induced” users to participate in unlawful behavior. Not so, Grady ruled.

“Craigslist does not ‘provide’ that information, its users do,” the judge wrote in his 22-page decision. “‘Facilitating’ and ‘assisting’ encompass a broader range of conduct, so broad in fact that they include the services provided by intermediaries like phone companies, [internet service providers] and computer manufacturers. Intermediaries are not culpable for ‘aiding and abetting’ their customers who misuse their services to commit unlawful acts.”

Grady also noted section 230(c)(1) of the CDA, which states websites that provide public sounding boards for users cannot be held liable for what users post, “would serve little if any purpose if companies like Craigslist were found liable under state law for ‘causing’ or ‘inducing’ users to post unlawful content in this fashion.”

Grady’s is not the first case against Craigslist to fail for that reason. In March 2008, a federal appeals court reached a similar conclusion after a housing-rights group sued the online classifieds giant over ads that indicated apartment leasing agents applied illegal ethnic bias against applicants.

Dart’s cause didn’t fall on entirely deaf ears, however.

“Sheriff Dart may continue to use Craigslist’s website to identify and pursue individuals who post allegedly unlawful content,” Grady ruled. “But he cannot sue Craigslist for their conduct.”