[Stephen]

You could say that any investigation into a person is a 'witch hunt'

They are investigating the claims made and will continue it until they either find enough evidence that proves the claims correct, or if while investigating come across other crimes and illegal activities conducted by others proceed with those or if nothing is proved it will be concluded.

They won't just shut down the investigation because the person at the centre of it claims there is nothing to find and protesting his innocence greatly and at every opportunity. Which in many cases goes some way to indicating they have something to hide.