There are doubts over the Royal Commission's plan to take public submissions over the mosque attacks.

Community groups, organisations and members of the public are invited to make submissions by email or letter.

The Commission is looking for information on what relevant agencies knew about the alleged shooter before the attacks and whether there was anything that could've been done to prevent them.

Chairperson Sir William Young says there are many who haven't come forward who may have experiences to share which can help the inquiry.

However, Massey University teaching fellow John Battersby told Mike Hosking the inquiry's scope is too narrow for this to help.

He says the terms of reference are centred around the security services and what could have been prevented and what can be prevented in the future. 

"I'm not quite sure what a community group or any particular group defined any which way has to offer that because those are the questions the Royal Commission has to answer and I'm not sure the rest of us can really contribute."

Battersby says that it could be a bit of public relations exercise, and he says it could be pointless as few members of the public would be able to offer insight into the issues.