Honolulu’s top prosecutor is dismissing cases against 16 women arrested in a massage parlor prostitution sting after the sex assault charges they faced drew criticism.

The women were arrested this month during an operation involving Honolulu police and federal authorities. But instead of being arrested on suspicion of prostitution, police accused the women of sex assault.

"Although the conduct might have constituted a technical violation of the law, proof beyond a reasonable doubt could not be established," Prosecuting Attorney Keith Kaneshiro said in a statement Wednesday. "Therefore, these cases were dismissed."

If convicted of sex assault, the women would have had to register as sex offenders and could have been sentenced to up to a year in jail, while a prostitution charge carries 30 days. At the time of their arrests, legal experts said the new tactic from the Honolulu Police Department is unusual for a law enforcement agency. Advocates for prostitutes and sex trafficking victims decried the arrests as re-victimizing the victims.

"I think the charges being dropped is a clear sign that this isn’t a method HPD should use," said Kathryn Xian, executive director of Pacific Alliance to Stop Slavery. "I think it’s been an embarrassing situation for law enforcement."

Hawaii has a strange history with prostitution investigations. Until a year ago, police officers were legally allowed to have sex with prostitutes as part of investigations. State lawmakers changed that policy last year after The Associated Press highlighted the loophole.

Myles Breiner, an attorney representing some of the women, said in at least one instance at a massage parlor called Orchid Relaxation, an officer disrobed, took the woman’s hand and put it on his genitals.

A woman who answered the phone at Orchid Relaxation declined to comment.

"They’re experimenting with the limits of the constitution," Breiner said after hearing that the charges were dropped. "Sex assault in the fourth degree is a nonconsensual touching of a sexual nature. How can you say it’s not consensual when the officers are going into these establishments intending to be touched?"

When asked if the department had any comment on Kaneshiro declining to prosecute the women, a police spokeswoman pointed to a letter posted on social media Tuesday.

"Some in the community have questioned the recent arrests of cosmetology and massage parlor employees, and more information will come out in court," the letter said. Arraignments were scheduled for Friday.

The letter went on to say that many officers feel uncomfortable enforcing prostitution laws, but have jobs to do.

"Because many prostitutes know that the police need a verbal agreement of sex for money before an arrest is made, they will routinely do a ‘cop check.’ This consists of initiating sexual contact to try to determine if a prospective john is an undercover police officer," said the letter, signed by Chief Louis Kealoha, U.S. Attorney for Hawaii Florence Nakakuni, Honolulu FBI Special Agent-In-Charge Paul Delacourt, Homeland Security Investigations Assistant Special Agent-In-Charge Frank Cabaddu and Kaneshiro. "Workers do this because they know that the officers are not allowed to initiate sexual contact."

Xian said she’s concerned that the arrests prompted deportation proceedings for some of the women who may have been trafficked here as sex workers.

"Every individual who is arrested is asked if she is a sex-trafficking victim," the law enforcement letter said. "Those who say yes and who are identified as victims are provided with immediate care, recognized as possible cooperative witnesses and directed to social services."