Revelations a school caretaker sexually abused girls as young as five have renewed calls for a public sex offender register.

64 year old Robert Selwyn Burrett is facing 21 charges including rape, after admitting abusing 12 primary school girls, some of who were mentally disabled.

He installed curtains and locks on a shed on school grounds to hide some of his offending.

Sensible Sentencing Trust's Garth McVicar said Burrett's criminal history is suppressed and it may not ever be revealed what he's done in the past.

He said police resources have been cut drastically.

"So I think the only way we can deal with that is the public need to be the eyes and ears of the police, see what's going on, I can't say it would have prevented this but we can categorically prevent a lot of the offending that is going on."