Turkish intelligence agencies are reportedly investigating the travels of the accused Christchurch gunman, as they suspect he may have been aided and supported by a "well resourced" organisation.
The man entered Turkey twice in 2016 - for a week in March and for more than a month in September.
Over the past eight years he had travelled several times to Europe, as well as other countries like Pakistan and North Korea.
Turkish authorities have begun investigating everything from hotel records to camera footage to try to ascertain the reason for his visits.
Senior politicians from Turkey have been meeting with New Zealand government representatives and are expected to spend the next few days in Christchurch.
Police and intelligence officials say his level of knowledge, and choice of destinations, is unusual for a person of his background and education.
The accused gunman did not enrol in tertiary education, getting a job in a local gym when he left school in the new South Wales town of Grafton.
Toygun Atilla, who is terrorism and security correspondent for major Turkish newspaper, Hurriyet, told the ABC that Tarrant's interest in the Ottoman Empire, which controlled much of Southeast Europe, Western Asia and North Africa between the 14th and early 20th centuries and its downfall, have raised suspicions.
"That kind of ordinary profile, that is not very well educated, and not rich ... this person cannot commit such a violent action on his own," he said.
"Turkish intelligence thinks there is a well-resourced organisation behind this."
Police in Greece and the Balkans are also reviewing information about Tarrant's travel through the region between 2016 and 2018.
Britain's MI5 is also investigating potential links between the accused man and domestic UK extremist groups.
The Sunday Times has reported that MI5 - which controls the United Kingdom's counter-intelligence and security - has taken the lead in the investigation.