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During a media conference today, Mr Bush gave further details of the police response during the attacks that killed 50 people at Al Noor and Linwood mosques.
He said within five minutes and 39 seconds of being notified the first responders were armed and on the scene and ready to respond and within 10 minutes the armed offenders squad was on the scene.
"Within 21 minutes the person that is now in custody was arrested."
Mr Bush said the person was apprehended on the way to another target. He would not say what the target was.
"We absolutely believe we know where he was going and we intervened along the way."
He said during the arrest of the suspect, officers seized assault rifles and at least one semi-automatic rifle.
Speaking about identifying the victims' bodies, Mr Bush said it was an absolute priority to return the victims to their families.
As of at 11.30pm yesterday 21 of the victims had been formally identified and by midday there will be a further six victims identified and available to their families.
"By the end of today we should have completed those identifications. But I have to say some of those victims will take a little longer."
"We do, of course, have other obligations, and the first one on behalf of the chief coroner and all of the coroners is to ensure absolute accuracy in that identification process," Mr Bush said.
"If we get it wrong, that's unforgivable," he said.
Six coroners including the chief coroner are on site.
Mr Bush said the other responsibility was the prosecution of the case.
"We must prove, for prosecution, the cause of death to the satisfaction of the coroner and the judge."
"You cannot convict for murder without that cause of death."
The investigation was an international one; the FBI are on the ground in New Zealand, Australian Federal Police, other Australian police and other jurisdictions overseas were being consulted.
The threat level remains at high.
"If there was a specific threat, we would make sure we communicated that," Mr Bush said.