As Germany mourns the death of at least five people after a vehicle intentionally plowed into a crowded Christmas market, authorities are working to understand the suspect behind the attack.

The suspect – identified by local media as 50-year-old Taleb A. – had been living and working as a psychiatry and psychotherapy specialist in Germany for two decades, authorities said.

Originally from Saudi Arabia, Taleb arrived in Germany in 2006 as was recognized as a refugee in 2016, CBS News partner BBC reported.

A Saudi source told Reuters that Saudi Arabia had warned German authorities about the attacker after he posted extremist views on his personal X account that threatened peace and security.

Taleb’s X account is filled with posts and re-shared posts focusing on anti-Islam themes and criticism of the religion while sharing congratulatory notes to Muslims who left the faith. He also described himself as a former Muslim.

He was critical of German authorities, saying they had failed to do enough to combat the “Islamism of Europe.”

He has also voiced support for the far-right and anti-immigrant Alternative for Germany (AfD) party.

Germany’s FAZ newspaper said it interviewed the suspect in 2019 and described him as an anti-Islam activist.

“People like me, who have an Islamic background but are no longer believers, are met with neither understanding nor tolerance by Muslims here,” he was quoted as saying. “I am history’s most aggressive critic of Islam. If you don’t believe me, ask the Arabs.”

Prominent German terrorism expert Peter Neumann posted on X that he had yet to come across a suspect in an act of mass violence with that profile.

Neumann, the terrorism expert, wrote: “After 25 years in this ‘business’ you think nothing could surprise you anymore. 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.”

Some described Taleb as an activist who helped Saudi women flee their homeland. Recently, he seemed focused on his theory that German authorities have been targeting Saudi asylum seekers.

On Saturday, German Interior Minister Nancy Faeser told reporters: “At this point, we can only say for sure that the perpetrator was evidently Islamophobic – we can confirm that. Everything else is a matter for further investigation and we have to wait.”

A German-based organization called Athiest Refugee Relief said the alleged attacker was not a part of the group and claimed that he made “numerous accusations and claims” against it and former board members, which it said were false.

“We distance ourselves from him in the strongest terms,” the group said in a statement on its website, adding that members of Atheist Refugee Relief filed a criminal complaint against him in 2019 following “the most foul slander and verbal attacks.”

Taleb was arrested on site after plowing a black BMW into a Christmas market crowded with holiday shoppers Friday evening in Magdeburg, killing at least five people and wounding about 200 others.