If someone confesses to something in the past..... and they have made an effort to actually repent of what ever the issue was it should stay between the clergy and the person.
Now on the other hand if it is a currently happening crime, or there is reason to think any one might be in danger due to the persons actions... the clergy member has a very clear moral obligation to go to the authorities.
The clergy going to the authorities should never be about making sure the person was punished... it should solely be to protect the innocent.