New Zealand police believe just one shooter was involved in separate deadly attacks at two Christchurch mosques just seven minutes apart.
At least 49 people were shot dead at prayers on Friday afternoon - 41 were killed in the first attack at the Central Mosque, while eight others died at the Linwood Ave mosque shortly after.
Australian man Brenton Tarrant, 28, on Saturday faced court on one count of murder. Further charges are likely to be laid before he appears again on April 5.
At a media conference on Saturday, NZ Police Commissioner Mike Bush was asked if the same person was involved in both scenes.
"It would be improper for us to go into the detail, now that a person has been charged, but I will say, because I want to be as informative as possible, that we know nothing that will contradict what you've just suggested," he said.
Another man and a woman are being questioned, but their roles - if any - are yet to be determined.
"We are currently working through whether or not that person or those persons had any involvement in this incident," he said.
He said there was no intelligence about imminent threats.
"But I would never assume anything in this situation. That's why it's so important that we resource the intelligence and investigations phase of this to make sure we understand everything and understand it urgently.
Australian authorities are helping their New Zealand counterparts with intelligence for the investigation.
NZ police have also defended the 36 minutes it took to arrest Tarrant, with some criticism that police were too slow too react to the attacks.
Mr Bush said police were at the first mosque in Deans Ave within minutes of the incident being reported at 1.42pm on Friday.
District Commander John Price, who was in charge of Friday's operation, told reporters on Saturday he was happy with the response.
"That is an incredibly fast response time. You had a mobile offender across large metropolitan city," Commander Price said.
Mr Bush praised police and other emergency service workers for their actions - and members of the public who tried to help.
He said the arrest of Tarrant was dangerous.
"That person was not willing to be arrested," Mr Bush said.
"We also believe that not only were there IEDs in that vehicle, so it was a very dangerous manoeuvre.
"There were also firearms in that vehicle, so our staff who were well-equipped, did engage with that person and again, put themselves in real danger to keep the community safe from further harm."