Women posting sex ads online in Northern Virginia are increasingly likely these days to be met by a cop instead of a customer.

Authorities say they have seen an uptick in prostitution at area hotels and are increasingly using stings to target the women. And although the number of arrests is still small, it’s on the rise.

“Were seeing an influx of prostitutes coming out from the West Coast,” said Lt. Kip Malcolm of the Arlington County Police Department.

Most of the arrested women had posted ads in the escorts section of Backpage.com, a Web site that has replaced Craigslist as the preferred site for selling sex. Police go to Backpage, find ads advertising escorts in the area and respond as “Johns.”

Prostitutes find the area attractive, police say, because it offers access to high-income customers as well as the highway. In Arlington, the activity is centered largely on hotels around Crystal City, Ballston and Rosslyn. In Alexandria, most of the arrests occur at hotels along Interstate 395 and Route 1, which police said make it easy for prostitutes to travel south through Virginia into North Carolina or north into the District. Some women even list the nearby roads in their ads.

In 2012, Arlington arrested 18 women on prostitution charges. In 2013, that figure rose to 32. Halfway through this year, there have already been 26 arrests. In Alexandria, according to court papers, 27 alleged prostitutes and five alleged pimps have been arrested in hotels or apartments. Each of those cases involved Backpage.com. Last year, there were only two similar cases.

A full accounting of cases from Fairfax County was not immediately available, but from March to mid-July, police made 18 arrests for prostitution-related activities.

The focus on such cases in Alexandria came, in part, after prosecutors in the fall won a 27-year-sentence against a Florida pimp under Virginia’s racketeering law, a case built in part out of hotel arrests. One arrested girl was 16 years old. Others testified that they were kept in line with threats and abuse.

“That was the case that kind of changed my outlook into the human-trafficking issue and convinced me that it was a serious problem in this city,” said Alexandria Commonwealth’s Attorney Bryan Porter. “I think people who kind of turn a blind eye to it and say, ‘Oh, it’s just some guy having sex for money’ don’t see the big picture.” Earlier this year, he spoke at a conference for state attorneys general about using the Racketeer Influenced and Corrupt Organizations Act (RICO) to go after pimps.

But police in both jurisdictions say they aren’t seeing many similar trafficking cases. Instead, many cases are “women that are working for themselves,” said Crystal Nosal, an Alexandria police spokeswoman.

“The ease of the Internet . . . kind of eliminates the need for the old-fashioned pimp,” Malcolm said.

Cyndee Clay agrees. Clay runs the pro-decriminalization group Helping Individual Prostitutes Survive (HIPS), a nonprofit based in the District. When her organization was formed in the early 1990s, she said, most prostitutes worked on the street and were dependent on pimps to secure territory. The rise of hotel-based work, she said, has in some ways “been an equalizer” that makes it possible for prostitutes to operate independently.

Bradley Myles, executive director of the Polaris Project, which fights trafficking, said that not all prostitutes have been forced or coerced into the trade but that many independent operators were first brought into it by a pimp. The organization is collaborating with Fairfax police and a state-federal task force to provide victim services in Northern Virginia.

“We want to make sure that the people who are selling sex are treated with compassion, care and sensitivity,” he said. “We see tons of examples of police departments arresting women in the sex trade and treating them like criminals, but not actually asking the deeper questions.”

Currently, Alexandria police are pursuing a case against two alleged pimps, Kenton Franklin and Garrett Treese. (Another arrested this year pleaded guilty and given a suspended sentence.) At a preliminary hearing for Franklin, prosecutors invoked human trafficking. The prostitutes with him during his arrest, who prosecutors said would not testify because they were too afraid, were also charged and found guilty.

In a recent court appearance, Franklin’s attorneys unsuccessfully argued to ban the words “human trafficking” from the trial. “It suggests something wholly different from pimping,” public defender Jasmin Mize said, which can be a “consensual business relationship.”

Law enforcement officials contend that trafficking — defined at the federal level as using “force, fraud or coercion” — can be subtle, involving drug dependency, false promises and implicit threats.

“There’s not necessarily force in the traditional sense,” said Bill Woolf, a Fairfax detective working with federal agents on the Northern Virginia Human Trafficking Task Force. “It’s more of the coercive nature.” Arrests across the area are rising, said Woolf, but it’s not clear if that’s the result of an increase in trafficking or in enforcement.

When gangs are heavily involved in the sex trade, they’re more likely to operate out of local homes and advertise by word of mouth than to use hotels and Backpage.com, Woolf said.

Although prostitution is explicitly banned in Virginia, the more common and easier-to-prove charge is of keeping, residing in or visiting a “bawdy place” — anywhere “lewdness, assignation or prostitution” occurs. Both are simple misdemeanors, and most cases end with a fine, if the accused even shows up to court. Pimping is a felony.

Clay, who supports decriminalization, says she has never heard a sex worker say that an arrest helped her leave the business. Instead, she said, having an arrest or conviction — even for a misdemeanor — makes it harder for prostitutes to find other work, and that attitude makes it harder to arrest traffickers.

“Even in those circumstances when we’ve talked to women under gang control, they’re very afraid of talking to police,” she said.

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