FOR YEARS, classifieds website Backpage.com has denied reports that it was involved in facilitating child sex trafficking and exploitation. It insisted that it was a passive host of third-party content and had no control over its sex-related ads — many of which featured children. Reporting from The Post’s Tom Jackman and Jonathan O’Connell raises new questions about these claims.

According to documents provided to The Post from an unrelated legal dispute, a contractor for Backpage in the Philippines has been aggressively soliciting and creating sex-related ads for the website. Emails from a Backpage.com address directed the contractor to find ads from rival websites and explicitly mentioned ads for “adult services,” suggesting that at least someone at Backpage was aware of the contractor’s activities. This revelation builds on the results of a recent Senate investigation, which found that Backpage was editing ads to remove language that explicitly referred to underage girls, rather than deleting the ads altogether. The website also advised users on how to conceal illicit activity from its screening process.

Experts have long alleged that ads published in Backpage play a major role in facilitating human trafficking, including of children. The National Center for Missing and Exploited Children estimates that 73 percent of the 10,000 child trafficking reports it receives annually involve Backpage in some way. The website faces pending litigation in California, Washington state and Florida, among other states.

Backpage touted its “extensive efforts to prevent, screen and block improper ads” in a 2015 court filing in the District. But instead of fully cooperating with authorities, it has repeatedly resisted official investigations into its practices. It refused to comply with a Senate subpoena to hand over documents last year and was unanimously held in contempt of Congress — the first time such an action was taken in over two decades. When it was finally compelled to shut down its adult ad section in January, it claimed that it had been “unconstitutionally censored.” Backpage has also filed lawsuits over state and federal laws that tackle online sex trafficking.

In response to the latest revelations, three senators have recommended the Justice Department conduct a criminal review. Legislators also are debating whether to amend the 1996 Communications Decency Act, which gives third-party hosts such as Backpage wide-ranging immunity for content posted by its users. This immunity has been vital to the development of free speech on the Internet, but can also provide a loophole for companies that tacitly facilitate human trafficking. It is for Congress to see if it can amend the act without infringing on First Amendment rights, or if passing some other preventive measure is more viable.

What is clear is that something must be done. At the Senate hearing on Backpage in January, Sen. Claire McCaskill (D-Mo.) remarked, “Children were sold, and they simply tried to sanitize it. That, ladies and gentlemen, is the definition of evil.” Given the contents of these new documents, we understand how she feels.