Police said they are conducting a full review of their undercover investigation policies, but said none of the three officers, whose actions during stings made convictions impossible, would be investigated, reported MPR News.

“The Minneapolis Police Department is taking immediate action by reviewing these cases,” Police Chief Janeé Harteau said in a statement. “We are no longer using undercover operations to investigate suspected prostitution in massage businesses.”

In one of the dismissed cases, a police officer was investigating alleged prostitution activities at a massage parlor. In an audio recording of his encounter with a suspect, he is heard asking the masseuse whether the woman wants him to roll over on his back. The woman then touches the man’s genitals. He moans before saying a code word for his backup to begin an arrest, reported the Star Tribune.

“The Police Department has undercover female officers who do detail like this,” Hennepin County chief public defender, Mary Moriarty commented on the case. “Do you think they would allow themselves to behave in any sort of sexual manner?”

In another case, also involving a massage parlor, an undercover officer negotiated a price for “taking care of him” while a female suspect was rubbing his genitals. The third case involved the same woman and another officer in a strikingly similar situation of negotiating a price during a massage of the officer’s private parts.

“My hope is that the Police Department will finally stop engaging in the outrageous conduct of having sexual relations with the targets of their investigations,” attorney Jeffrey Dean, who represented the woman in both cases, said.

“Women in prostitution are vulnerable and traumatized. They have often been the victims of physical and sexual abuse and suffer from poverty and addiction. When police engage in this unnecessary sexual conduct, the officer worsens the trauma and deepens the damage,” he added.

Apparently, Minneapolis PD failed to properly instruct its officers on the law, as they said they believed their actions were necessary to build a case. In fact, the opposite is true, as ruled by the Minnesota Court of Appeals six years ago.

The 2009 decision stated that sexual conduct with a suspect during a sting is “outrageous conduct in violation of the guarantees of due process in the United States and Minnesota constitutions” and “unnecessary to any reasonable investigation.”

Dean noted that six years later “the very same police department, even with that clear notice, continues to engage in the same outrageous conduct.”

Police prostitution stings drew nationwide public attention last year in Hawaii, when it emerged that state law made it legal for officers to engage in sex with prostitutes. The exemption allowing such conduct was initially preserved in a new bill designed to crackdown on the sex trade, but after public outcry lawmakers decided to drop it.

Prostitution is illegal in the US, with the exception of several counties in Nevada. Human rights activist say the continued criminalization of the trade victimizes prostitutes, many of whom are victims of human trafficking, are often abused physically and sexually, and suffer from drug addiction and poverty.