A police officer in charge of investigating allegations of child sexual abuse by Hunter Valley Catholic priests has denied saying there was no prospect of convicting anyone of covering up the crimes.

Detective inspector David Waddell told a state government special commission of inquiry on Monday that he "definitely" made no such comment to a sex abuse investigations officer under his command in 2010.

"I don't recall the specifics of the conversation at all," Inspector Waddell said.

"We hadn't conducted an investigation at that stage but some key persons were deceased and that was a problem.

"I think the outcome (of any investigation) could not be predetermined, an investigation would have to take place," he said.

The inquiry had heard details of an email sent on May 20, 2010 from state sex crimes squad Detective Inspector Paul Jacobs to Detective Brad Tayler.

"From what I understand from Dave Waddell, although this inquiry/assessment may have to be handled with diplomacy there is no prospect of any criminal investigation outcomes as key persons (that is the offender and decision maker within the church) are both deceased," Det Insp Jacobs wrote in the email.

The special commission of inquiry into allegations of child sex abuse by Hunter Valley Catholic priests, which began in Newcastle six days ago, is focusing on how police and church officials handled the allegations.

It is particularly looking at allegations involving serial sex offender Father Denis McAlinden and convicted paedophile Father James Fletcher, who are both now dead.

It is also looking at the circumstances surrounding Detective Chief Inspector Peter Fox being stopped from investigating such matters.

Inspector Waddell, who was based at Lake Macquarie at the time, said he was overseeing an average of 500 police matters which included up to 100 cases in his detectives' office.