On Friday, online accounts linked to gun attacks that claimed lives of 49 people and injured at least 20 at two New Zealand mosques had in recent days circulated white supremacist imagery and extreme right-wing messages celebrating violence against Muslims and minorities on social media and message boards.
A gunman broadcast live footage on Facebook of the attack on one of the mosques.
According to the police, 4 people were in custody and one had been charged with murder over the country`s worst ever mass shooting.
On Wednesday, the Twitter handle @brentontarrant tweeted pictures of one of the guns later used in the mosque attacks in the city of Christchurch. It was covered in white lettering, featuring the names of others who had committed race- or religion-based killings; Cyrillic, Armenian and Georgian references to historical figures and events; and the phrase: "Here`s Your Migration Compact".
The number "14" was written on the side of the rifle as well, a reference to the "fourteen words", a white supremacist mantra.
A person involved with the attacks also appeared to post regularly to the "/pol/ - Politically Incorrect" forum on 8chan, an online discussion site known for allowing virtually any content, including hate speech.
About 1:30 p.m. (0030 GMT) on Friday, the anonymous user told the group "I will carry out an attack against the invaders, and will even live stream the attack via Facebook"; approving responses to the post included Nazi images and memes.
"Social media has certainly shifted global security risks," said Anwita Basu, an analyst at the Economist Intelligence Unit. "More than anything, social media has provided a platform for sharing extremist views."
"Police alerted us to a video on Facebook shortly after the live stream commenced and we quickly removed both the shooter`s Facebook and Instagram accounts and the video," Facebook tweeted. "We`re also removing any praise or support for the crime and the shooter or shooters as soon as we`re aware."
YouTube, which is owned by Google, tweeted: "Our hearts are broken over today`s terrible tragedy in New Zealand."
"Twitter has rigorous processes and a dedicated team in place for managing exigent and emergency situations such as this," the company said in an emailed statement. "We also cooperate with law enforcement to facilitate their investigations as required."