Bush said the man was apprehended 36 minutes after police were alerted.
Officials in New Zealand have not yet released the names of those killed or wounded, but Prime Minister Jacinda Ardern said on Friday that many of those "directly affected by this shooting may be migrants to New Zealand" or even refugees.
The tragic attack saw 41 people killed at the Masjid Al Noor mosque in central Christchurch, whilst seven others were killed at the suburban Linwood Masjid Mosque, and one person died later at Christchurch Hospital.
Thirty-four people were in Christchurch Hospital, with 12 in intensive care, while one child was moved to a dedicated children's hospital in Auckland. He is due back in court on April 5 and police said he was likely to face further charges.
"But that arrest was tangential to this matter and we do not believe that he was involved in this attack either", he said.
Ms Ardern confirmed her office was one of about 30 that had been sent the manifesto nine minutes before last Friday's massacre, but it did not contain details of where the attacks would take place. Two other men remain in custody, although their link to the attack is unknown.
"The police has been telling us for several years that their big, rising concern - which they struggled to put resources at because it's not an immediate threat - is the rise of right-wing extremism", Barton said.
They included Asif Shaikh, 44, who said he was among more than 100 people at the Al Noor mosque when the attacker came in.
Meanwhile, people across New Zealand are reaching out to Muslims in their communities and around the country the day after mass shootings.
Unlike the US, the right to own a firearm is not enshrined in New Zealand's constitution.
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He added the forecasts are "predicated on a fairly smooth transition, they're certainly not predicated on crashing out without a deal".
'I can tell you one thing right now, our gun laws will change, ' Ardern said.
"The United States strongly condemns the attack in Christchurch".
The youngest person missing and feared dead is three years old, Greenhill tells NPR's Weekend Edition.
He said he survived by playing dead, but was desperate to know what happened to his friends who were there with him.
Leaders around the world expressed sorrow and disgust at the attacks, with some deploring the demonisation of Muslims.
Tarrant lived in Dunedin, on New Zealand's South Island, and was a member of the Bruce Rifle Club, according to media reports which quoted club members saying he often practiced shooting an AR-15, which is a lightweight semi-automatic rifle.
"Across all religions, our houses of worship are a source of refuge, of prayer, and of love; to see such a heinous and hate-filled act occur in what should be places of peace is the darkest of evils".
This senseless attack is an affront to the people of Christchurch and New Zealand, and the broader Muslim community.
Pence also affirmed US cooperation in ensuring all the perpetrators were brought to justice.