Honolulu's top prosecutor is dismissing sex assault charges against 16 women who were arrested in a massage parlor prostitution sting.

Prosecuting Attorney Keith Kaneshiro said Wednesday that the allegations might have constituted a technical violation of law, but proof beyond a reasonable doubt couldn't be established.

The women were arrested earlier this month, but instead of being arrested on suspicion of prostitution, police accused them of sex assault.

Legal experts say that tactic is extremely unusual.

The Honolulu Police Department didn't immediately comment on the charges being dropped.

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