The embattled CEO of Backpage.com, Carl Ferrer, was arrested Thursday and accused of running an online ad portal that facilitated prostitution and the pimping of young children into sexual servitude.

"Raking in millions of dollars from the trafficking and exploitation of vulnerable victims is outrageous, despicable, and illegal, California Attorney General Kamala Harris said. "Backpage and its executives purposefully and unlawfully designed Backpage to be the world’s top online brothel."

Charged with a variety of felonies, (PDF) including pimping a minor, pimping and conspiracy to commit pimping, is Carl Ferrer. The 55-year-old Ferrer has been in a year-long battle with the US Senate, which voted to hold him in contempt for his refusal to comply with an investigation into online sex trafficking. He had claimed the Web portal enjoyed a First Amendment right not to supply documents to the Senate Subcommittee on Investigations about how it reviews third-party ads posted to the site. After his legal challenge ping-ponged through the courts, the US Supreme Court last month approved the subpoena, forcing Ferrer to comply.

A Senate investigation has also said it found "substantial evidence that Backpage edits the content of some ads, including deleting words and images, before publication. The record indicates that in some cases, these deletions likely served to remove evidence of the illegality of the underlying transaction."

Ken Paxton, the Texas attorney general, said Ferrer was arrested on a California warrant after he landed in Houston on a flight from Amsterdam. Ferrer's arrest, and the charging of two controlling shareholders—Michael Lacey and James Larkin—on conspiracy to commit pimping, culminates a three-year joint investigation by the states of Texas and California. The site's Dallas headquarters was raided by the authorities on Thursday.

According to the California Department of Justice:

While Backpage hosts ads for sales of a range of items and services, the arrest warrant (PDF) alleges that the vast majority of Backpage’s revenue is generated through prostitution-related ads in its “adult services” section. Backpage collects fees from users who post “escort” ads, offering sex for money using coded language and nearly nude photos. The California Department of Justice’s investigation found that many of the ads for prostitution services involved victims of sex trafficking, including children under the age of 18.

Court documents in the case quoted children saying they were forced into prostitution, with their services advertised on Backpage. Harris said that 99 percent of Backpage's worldwide income "was directly attributable to the "adult" section. Between 2013 to 2015, Backpage generated $51 million in revenue in California alone, Harris said.

The National Center on Sexual Exploitation on Friday called Ferrer the "Global Kingpin of Pimping."

"Backpage’s profiteering from sex trafficking and prostitution is equivalent to the East India Company’s facilitation of the African slave trade," Dawn Hawkins, the executive director of the National Center on Sexual Exploitation, said.

In California, pimping amounts to profiting off of prostitution.

The National Center for Missing and Exploited Children said reports of child sex trafficking, most of it online, have increased more than 800 percent over a five-year period.

Backpage, which the three accused men founded in 2004, did not immediately respond for comment. The site was up and running on Friday, hosting tens of thousands of "adult" ads with categories including "escorts," "body rubs," "dom & fetish," and "male escorts."