A former Communist-era intelligence chief in Bulgaria has criticised his country's security services for not better monitoring the alleged Christchurch shooter during a six-day tour of the eastern European state, four months before the attacks.
The comments come as Balkan governments continue to investigate Brenton Tarrant's movements during two visits to the region in 2016 and 2018.
Last week, Austrian authorities uncovered a $NZ2480 donation he had made to a far-right extremist group early last year.
The ABC has confirmed that Australian and New Zealand security services made formal requests of Bulgaria to trace Tarrant's movements, and that the first inquiries were made within 24 hours of the Christchurch atrocity.
On 15 March, 50 people were killed when the gunman stormed two mosques in Christchurch with a number of high-powered guns.
The accused man live-streamed the attack online and posted a rambling "manifesto" describing his motivations.
Colonel Slavcho Velkov, who until two weeks ago was the deputy chairman of the Bulgarian Parliament's intelligence and security committee, said there were far-right nationalist groups in Bulgaria, but that Tarrant appeared not to have made contact with them.
"The Bulgarian services were asked by the services of Australia and New Zealand to retrieve and provide information regarding his itinerary in Bulgaria and whether he has had any contacts," he said.
"And they delivered. His itinerary across the country was located, no contacts were detected."
All hotels in Bulgaria are obliged to register the arrival of foreigners in a central database, which enabled security officers to swiftly identify the accused man's movements.
Security controls better during Communist era, major says
But the former security services boss in the Black Sea city of Varna, Major Pavlin Pavlov - who advocates for a return to the tight security controls of the Communist era - said the intelligence service should monitor foreigners more closely when they enter the country.
"Our services do not succeed to work properly as they once did," he said.
"We know only what we can get from the technical equipment available from the mobile operators and the border police, we know from where and how Tarrant entered and which sites he visited.
"But we do not know whom he met, what he ate and drank … what his behaviour was. This is exactly because of a gap in the system."
Major Pavlov told the ABC the country had so prioritised the threat of Islamic terrorism it had failed to properly monitor the rising threat of far-right extremism.
"Our services ... fail to grasp and forecast the trends in terrorism," he said. "The focus of course is on Islamic terror. But it is only natural that due attention should be paid to the other side of terrorism."
The ABC retraced some of the alleged shooter's movements through Europe and visited the guesthouse in Pleven, two hours north of Sofia, where he stayed.
The town is most famous for being the site of a major battle during the Russian-Turkish war of 1877 and 1878. Now, much of the town appears impoverished and it is littered with abandoned factories and apartment buildings.
The Kachaka Guesthouse, where Tarrant stayed during his visit, is surrounded by older apartment buildings, some of which are graffitied by swastikas and other Nazi symbols.
Owner Yordan Kacharmazov said he was surprised to receive the booking. He said Tarrant was his first guest from Australia and that "we had to communicate with gestures and signs".
"At the beginning I did not pay any special attention to him," he said. "He appeared a bit cold and reserved, but I thought this was his character."
The only feature that stood out to Mr Kacharmazov during the man's stay was his passport.
"On the top of the page I opened I saw 'The Islamic Republic of Pakistan'," he said.
"So, I had this gut feeling suddenly that kind of made me a bit nervous. So I started asking myself whether everything here was normal or not."
Within 24 hours of the Christchurch shootings, and before Mr Kacharmazov had realised who was allegedly behind the attack, he received a call from the Bulgarian intelligence services who asked questions about the man's visit.
"When they told me the real reason for calling me, all the pieces of the puzzle in my head came together," he said.
"There was one question, which was the main goal of all the investigations that have been conducted concerning his stay in Pleven ... [which] is why he has been on the territory of Pleven, whether he has any allies here, people with whom he can share his ideas."
Mr Kacharmazov said he and his friends in Pleven were appalled by the accused shooter's actions. He called it "pure sadism" and "pure insanity".
Tarrant travelled to 11 semi-rural locations in Bulgaria last November, all of which played witness to significant roles in the Ottoman wars more than 140 years ago, before crossing the border into Romania, and then travelling on to Austria.
Ten months prior, he had made a $NZ2480 donation to the Identitarian Movement, which as a result is under investigation by Austrian authorities.
The Austrian Chancellor Sebastian Kurz has announced he intends to try to forcibly dissolve the group.