From the Aussie Criminals blog I found this link to info about suppression orders
http://www.austlii.edu.au/au/legis/sa/consol_act/ea192980/s69a.html
EVIDENCE ACT 1929 - SECT 69A
69A—Suppression orders
(1) Where a court is satisfied that a suppression order should be made—
(a) to prevent prejudice to the proper administration of justice; or
(b) to prevent undue hardship—
(i) to an alleged victim of crime; or
(ii) to a witness or potential witness in civil or criminal proceedings who is not a party to those proceedings; or
(iii) to a child,
You can read more if you are interested.
I think we can dismiss the reasons in part (b) as there is no alleged victim alive, there is no witness who was not a party to the crime, and there is no child involved.
Therefore, the ongoing reason for a suppresion order must be (a) "to prevent prejudice to the proper administration of justice".
Then I found this site
http://www.judcom.nsw.gov.au/publications/benchbks/civil/non-publication_and_suppression_orders.html about suppression orders.
Here is a bit of it
"In most cases, non-publication orders are not granted to avoid the possibility that pre-trial publicity may prejudice an immanent trial. The risk that the publicity may cause the trial to be unfair would have to be “wholly exceptional” to satisfy the test of necessity. Even in cases which have attracted intense media attention non-publication orders have been refused. "
then further down
"Mere belief that an order is necessary is not sufficient, there must be some material before the court upon which it can reasonably reach the conclusion that it is necessary to make an order prohibiting publication. "
So I am still at a loss to know what material could be before the court that makes it reasonable to impose a suppression order.
If we assume (as some here do) that the police have compelling forensic evidence that proves the person they arrested was the killer, the suppression order makes no sennse at all, given the strict guidelines.
The police have stated there was only one killer, so the suppression order is not to protect a third party.
The only reason I can see for the suppression order is actually to protect the person they have arrested because the do not have sufficient evidence to be absolutely certain they have arrested the right person.