"the get-togethers were held in public places around Detroit"
...
"The FBI said those sites have been advertising for prostitutes in Ohio, Indiana, Illinois and many other states along with Windsor."
That's why the FBI was involved, I think..
But I found this part quite funny:
"Because they vet the people out, that's a way to keep the press and law enforcement away from them. If we were to try to slip in a police officer, it would be hard."
I'm sure there would be no shortage of male cops willing to go undercover.