Why can't they do some old fashioned police work and interview the girls? Get a warrant and physically monitor his movements to catch him visiting them, or them visiting him? You know... investigate. It's what we pay you to do.
They don't get to treat every single one of us as criminals just because they can't be bothered getting off their arses and doing some work. If I tried to make that excuse to my boss (and I'm public sector like them), they'd laugh at me and tell me to get to work or find a new job.