http://thefreethoughtproject.com/cops-sex-human-trafficking-victims/Years ago it was widely known in New York that police would go out and have sex with a hooker then arrest her. In fact that was a lot of the work vice cops did, have sex with hookers then arrest them.
Being a vice cop in NY when that was the practice obviously was considered a plum job. Go to work, have sex, collect your paycheck.
Now people are more into the subtleties of prostitution, like human trafficking, girls who are forced or bonded into prostitution, sometimes kept imprisoned in secure buildings in the U.S. In many places these operations are well known, and patronized by police.
Obviously now if Michigan cops are allowed to have sex with victims of human trafficking there will be "ongoing" investigations of human trafficking in that state that will last many years.
The police will always be 'close to making a case', but they will need a little more evidence so the investigations will go on and on.