Six were identified in a multi-state sex trafficking ring Monday afternoon, which included residential brothels in Bellevue and Kirkland. That same day, four plead not-guilty in U.S. District Court after a grand-jury indictment brought to a head a years-long investigation.

“These defendants exploited vulnerable women immigrants to enrich themselves,” said U.S. Attorney Jenny A. Durkan in a release. “We will work with our partners to stop this exploitation.”

Unruean Aboulafia, a 34-year-old Bellevue resident, believed to be working with her ex-husband, has been accused of leading the operation, managing advertisements on the controversial website backpages.com. Apartments were leased in Bellevue, Kirkland, Chicago; Scottsdale, Ariz. and Falls Church, Va. Charging papers indicate that many of the women were from Thailand and were here illegally, having overstayed their tourist visas. Among them is Aboulafia, herself a Thai national.

Human trafficking has been of growing concern in Washington state, and in particular on the Eastside. A number of cases involving immigrants have come to light in recent years. They are often at a greater risk, says Marie Hoffman of the Washington Anti-Trafficking Network, because of language and cultural barriers, a general mistrust or misunderstanding about law enforcements’ role and due to immigration status. Brothel operators may withhold paperwork and threaten to report them or harm their families.

“That prevents somebody from leaving the situation and creates an environment of fear,” says Hoffman.

Emily Langlie, spokeswoman for the U.S. Attorney’s Office, said that the victims and witnesses of the ring numbered in the dozens. According to charging papers, the women were lured to the U.S. with the prospect of work, and owed debts of as much as $60,000. An investigation was launched in 2009 after a complaint was made to Kirkland Police about suspicious activity in one of the Eastside residences. Undercover officers have been responding to the ads in an extensive investigation through February of this year. In most cases the women offered sexual favors for a fee, and on several occasions admitted to traveling to the U.S. to prostitute themselves for money.

“This case is more than prostitution, money laundering, and conspiracy,” said King County Sheriff John Urquhart. “It is about human trafficking.”

Charging papers reveal that the advertisements used code language like “160 roses/200 roses” to indicate pricing, and often pictured the women in skimpy clothing and suggestive poses. Ads were placed in the adult entertainment section of backpages.com under the labels of “escort” and “body rubs.” Among the Bellevue locations identified are the Belcarra Apartments, Amli Apartments, Avalon Bellevue Apartments and the Courtyard Off Main, all prominent buildings in the city’s downtown.

“This is a crime that happens in our community,” said Hoffman about the concerning rates of trafficking on the Eastside, “that affects people from all over the world, including the U.S., regardless of background, where they grew up or what community they live in.”

Hoffman adds that it’s not unusual to see female traffickers.

Aboulafia is charged with money laundering, conspiracy to use a communication facility to promote prostitution, conspiracy to transport individuals for prostitution and for the use of cellphones to advertise and facilitate services. Also indicted are Thanyathorn Mohr, 35, of Bellevue, alleged to have scheduled and directed clients; Xinping Zhang, 39, of Bellevue, accused of renting apartments and collecting funds; Jeff Chu, 48, also a resident of Bellevue and Chu’s ex-husband, for leasing apartments in Washington and Illinois; and Steven Aboulafia, 59, Unruean’s ex-husband of Henderson, Nev. Finally, Edward Flanigan, 57, of Federal Way, is accused of renting apartments in Washington and Virginia and is believed to have been a client of the prostitution ring.

The King County Sheriff’s Office, the Kirkland and Bellevue Police Departments and U.S. Immigration and Customs Enforcement’s (ICE) Homeland Security Investigations were involved in the investigation.

Mohr, Zhang and Chu pled not guilty alongside Unruean.