Then initiate actions to identify them. I am sure they left some sperm and other traces of their presence behind. They must have know the customer because they came to his house. Perhaps some immunity could be offered in return for the information.
I know this will be hard for you, but let’s imagine that the girl didn’t get paid and made up a story about three other men and a gun.
We here on FR, simply do not have the full story, nor the complete testimony. There are no other suspects. The police have not identified any. And for this you want the Judge’s hide (and mine). Okay, whatever. But if we are going to talk about the “rule of law,” the rule hasn’t necessarily proven a rape occured, at least in the mind of a legally appointed judge.