Police have raided two homes in Australia as part of the investigation into the attacks on two mosques in Christchurch, New Zealand.
Fifty people died and dozens were injured in the twin shootings on Friday.
Australian Brenton Tarrant, 28, has been charged with murder. He is believed to have acted alone in carrying out the attacks.
The suspect came from Grafton, 600km (370 miles) north of Sydney.
Authorities in New South Wales searched unidentified properties in the nearby suburbs of Sandy Beach and Lawrence on Monday morning.
"The primary aim of the activity is to formally obtain material that may assist New Zealand Police in their ongoing investigation," said New South Wales police.
Australian media reported that one of the homes belongs to Brenton Tarrant's sister. Police said his family in Australia were assisting with enquiries.
On Sunday, two members of the Tarrant family in Grafton told media they were "gobsmacked" by the shootings.
"We are so sorry for the families over there, for the dead and injured," uncle Terry Fitzgerald told Nine News.
Suspect may represent himself in court
Brenton Tarrant appeared in a New Zealand court on Saturday on a single murder charge.
He has since fired his lawyer and plans to represent himself at court at his next hearing in April, according to the New Zealand Herald.
"What did seem apparent to me is he seemed quite clear and lucid, whereas this may seem like very irrational behaviour," his former lawyer, Richard Peters, told the newspaper.
New Zealand's Prime Minister Jacinda Ardern has pledged to change gun laws following the nation's worst mass shooting.
Mr Tarrant legally owned five guns and had a firearms licence. He did not have a criminal record and had not been on the radar of security services in New Zealand or Australia.