""The reality of some police having sex with sex workers during the course of undercover operations has been in existence as long as selling sex has been a criminal offense," explains Dr. Alexandra Lutnick, an expert on the US sex industry at RTI International, a nonprofit research institute. A research study that she conducted in San Francisco found that over 14 percent of sex workers said that they had been threatened with arrest unless they had sex with a police officer, and two percent had been arrested after having sex with an officer anyway."