New Zealand Prime Minister Jacinda Ardern said her office received a "manifesto" from the gunman suspected of killing 50 people in two Christchurch mosques minutes before Friday's attack.
"I was one of more than 30 recipients of the manifesto that was mailed out nine minutes before the attack took place," Ms Ardern told reporters on Sunday.
"It did not include a location, it did not include specific details," she said, adding that it was sent to security services within two minutes of receipt.
Australian Brenton Tarrant, 28, a suspected white supremacist, was charged with murder on Saturday. Tarrant was remanded without a plea and is due back in court on April 5 where police said he was likely to face more charges.
Ms Ardern said she had read "elements" of the lengthy, meandering and conspiracy-filled far-right "manifesto".
"The fact that there was an ideological manifesto with extreme views attached to this attack, of course, that is deeply disturbing," she said.
The massacre was live-streamed around the world by the gunman and the shootings have raised new questions about violence being disseminated online.
Ms Ardern told the briefing that she had been contacted by Facebook operations chief Sheryl Sandberg who had acknowledged what had happened.
"This is an issue that I will look to be discussing directly with Facebook," Ms Ardern said.
Facebook said on Twitter it had removed 1.5 million videos of the attack in the first 24 hours and it was also removing all edited versions, even those without graphic content.
Tom Watson, Labour’s deputy leader, demanded social media sites freeze their websites in the event of a terrorist atrocity to prevent people sharing graphic images of terrorist violence.
He said a “radical rethink” was needed after Tarrant broadcast live the shootings on Facebook before it was shared among millions of people.
“If social media sites can't stop the videos being uploaded to their platforms then they should suspend all uploads,” he said. “If you have to review a massacre to assess whether it breaches your terms and conditions you've got the wrong business model.”
For almost three days forensics teams have been working through multiple crime scenes - at the Al Noor and Linwood mosques as well as a house in Dunedin, the southeastern city where the Tarrant lived.
Bodies of those he gunned down had remained inside the mosque awaiting autopsies and identification by increasingly distraught family members desperate to begin Muslim burial rites.
Ms Ardern tried to reassure them on Sunday.
"I can confirm that the bodies of those who have died are beginning to be returned to their families from this evening," she said, adding that all were expected to be released by Wednesday.
It is customary in Islam to bury the dead within 24 hours.
Ms Ardern said police would be posted at all mosques while they are open.
Police Commissioner Mike Bush earlier said the body of the 50th victim was found at the Al Noor mosque, where more than 40 people died after a gunman entered and shot at people with a semi-automatic rifle with high-capacity magazines, before travelling to a second mosque.
As the bodies of some victims were released to their families, a list circulated by relatives showed they ranged in age from three to 77 and included at least four women.
Amid the sadness, there have also been tales of heroes such as Alabi Lateef and a fellow worshipper, who followed the 28-year-old Australian gunman to his car and used a discarded rifle to smash the vehicle's back window.
Alabi said he told worshippers to duck down and then described how he and a "brother" decided to confront the attacker during a lull in the gunfire.
"By the time he got there (outside the mosque) the bullets were finished and the gun was used," Lateef recounted.
The pair's actions may have helped saved further casualties, as Tarrant was apprehended by two armed police officers soon after.
Daoud Nabi, a 71-year-old Afghan man, reportedly ran into the line of fire to save fellow worshippers at the Al Noor mosque and died shielding someone else from a bullet.
"He jumped in the firing line to save somebody else's life and he has passed away," his son Omar told AFP.
The mosque attacks have shaken this usually peaceful country, which prides itself on welcoming refugees fleeing violence or persecution.
Ms Ardern has vowed to change the country's gun laws and to uncover how a self-avowed extremist legally purchased two semi-automatic weapons, reportedly AR-15s, two shotguns and a lever-action gun without drawing the attention of the authorities.
It has also has emerged that a former soldier raised concerns about extremism at Tarrant's gun club in Dunedin.
Ardern said the cabinet would be briefed on Monday on the aftermath of the disaster and begin discussions "around issues like, for instance, gun policy."