Germany Searches for Motives in Christmas Market Attack

A frequent critic on social media of the German government, as well as of radical Islam. A reclusive neighbor who appeared to live most of his life on the internet. A man whose extreme political postings online prompted an alert to Germany from Saudi Arabia.

Officials in Germany were trying on Sunday to piece together the complicated profile of the man in custody suspected of killing five people by driving an S.U.V. into a crowd at a Christmas market two days earlier, an attack that has stunned the country.

The authorities have described the suspect as a 50-year-old Saudi doctor who had been living in Germany for nearly two decades. They say they are still trying to determine his motives. The Salus Clinic in Bernburg, a town about a half-hour drive from Magdeburg, said that the man worked as a psychiatrist in their closed ward, treating offenders who suffer from drug addiction.

The victims in the assault, which took place in the eastern city of Magdeburg, were a 9-year-old boy and four women aged 45 to 75, the police said in a statement on Sunday.

More than 200 others were wounded, 41 of them seriously, in the attack that shattered the peace of Germany’s Christmas season, which is celebrated in hundreds of outdoor markets around the country.