Australian Brenton Tarrant is a 28-year-old body builder and personal trainer from the small town of Grafton in northern New South Wales.
After his father's death in 2010 from cancer, he invested in cryptocurrency, quit his gym job and took a tour through North Korea, Pakistan, Turkey, Eastern Europe, France and elsewhere.
Ankara on Friday said it was investigating Tarrant's multiple visits to Turkey, and who he might have met while he was there. The Bulgarian government has also said it was looking into Tarrant, who apparently visited the country late last year.
Tarrant's 74-page manifesto said he first began considering an attack in April and May of 2017 while travelling in France and elsewhere in Western Europe.
London's Independent newspaper said he allegedly met right-wing extremists during a visit to Europe that year and declared allegiance to a group he called Europeans. Tarrant also claimed he contacted an anti-immigration group called the reborn Knights Templar.
He planned not only the two-site murder rampage but also the manifesto and a social media campaign, which included his newly created Twitter account, full of links to white supremacist and anti-immigration postings.
He created a musical soundtrack for his attack, curating martial music from Russia, Serbia and Britain.