The man suspected of driving a car into a crowd at a Christmas market in Magdeburg shared posts on social media in support of the AfD, Elon Musk and Tommy Robinson.
The death toll in Germany has risen to five with more than 200 injured after a BMW was driven at speeed through a large crowd on Friday night.
The suspect, named in reports as Taleb al-Abdulmohsen, is a Saudi doctor in his 50s, officials have confirmed.
He arrived in Germany in 2006 and has worked in the Saxony-Anhalt region.
Al-Abdulmohsen, who was seen being arrested by police on Friday, is an anti-Islam ex-Muslim who has reportedly helped other Saudis flee the country.
He has been recognised as a refugee since 2016.
MailOnline reports that the suspect is a specialist in psychiatry and psychotherapy from the Saudi Arabian city of Hofuf.
An analysis of his social media use shows that he has previously posted in support of the AfD, the far right party that has seen a surge in support in recent years.
Other posts expressed support for Tesla and X boss Elon Musk, far-right activist Tommy Robinson and conspiracy theorist Alex Jones.
His social media bio said: “@Saudi Military Opposition. Germany chases female Saudi asylum seekers, inside and outside Germany, to destroy their lives. Germany wants to Islamize Europe.”
In one post, he said: “Can you find one positive thing about Islam?”
In June, he retweeted a post that said: “The left are crazy. We need the AfD to protect the police from them.”
Der Spiegel reports that the suspect said in an interview: “If you listen to someone like Tommy Robinson or even Elon Musk, and even if you are ignorant of the process of Islamization, you will think that they are both conspiracy theorists.
“But I can say from experience that everything Robinson says, what Musk says, what Alex Jones says, or anyone who is described by the mainstream media as a radical or right-wing extremist – they are telling the truth.”
The comments appear to be from an interview with an organisation called Rair Foundation USA. The interview was shared on X but it is not clear when the interview was held.
Al-Abdulmohsen also quoted a tweet from Dutch far-right politician Geert Wilders and said: “The real hero is this man.”
Mr Wilders original post said: “Islam is a lie. Mohammed is a criminal. The Koran is poison.”
Peter Neumann, an expert in terrorism at King’s College, London, wrote on X: “After 25 years in this business, you think nothing could surprise you any more.
“But a 50-year-old Saudi ex-Muslim who lives in East Germany, loves the AfD and wants to punish Germany for its tolerance towards Islamists – that really wasn’t on my radar.”
Tesla boss Mr Musk has been a vocal critic of German Chancellor Olaf Scholz. Earlier this week, he said “only the AfD can save Germany.”
Elon Musk and Tommy Robinson have been approached for comment.
