German authorities said they received tipoffs last year about the suspect in a car attack at a Christmas market in Magdeburg as more details emerged on Sunday about the five people killed.
Authorities have identified the suspect as a Saudi doctor who arrived in Germany in 2006 and had received permanent residency.
Police haven't publicly named the suspect, in line with privacy rules, but some German news outlets have identified him as Taleb A. and reported that he was a specialist in psychiatry and psychotherapy.
Authorities say he does not fit the usual profile of perpetrators of extremist attacks. He described himself as an ex-Muslim who was highly critical of Islam and in many posts on social media expressed support for the far-right anti-immigrant Alternative for Germany (AfD) party.
He is being held in custody as authorities investigate him.
The head of the Federal Criminal Police Office, Holger Mnch, said in an interview on the German broadcaster ZDF on Saturday that his off