>>unable to prove him guilty..."
She doesn't have to prove anything. ?It's not her job. All she has to do is report the missing people and her suspicions, provide clues and probable cause for the police to investigate.
And surely she isn't the only one who has noticed or would go to the police. ?Parents of the missing students would surely be calling the police.
I, for one, don't find the setup credible that with a pack of concerned parents screaming at them to find their kids. the police would fail to vigorously investigate, would ignore or discount any clue anyone brings forward.