German authorities on Saturday were searching for a motive that they said led a driver to plow an SUV into a crowd at a Christmas market set up in a narrow alley in the eastern city of Magdeburg on Friday evening, killing at least four people and injuring more than 200 others.

Memorials were planned for Saturday, and Chancellor Olaf Scholz was expected to visit the site of the attack, which came as many Germans were marking the start of the Christmas holiday after a year of gloomy news about a slowing economy and the collapse of the German government.

The authorities said the driver of the SUV was a 50-year-old citizen of Saudi Arabia who had lived in Germany for decades on a visa that granted him permanent residency. The news provided more fuel for the polarizing debates over uncontrolled immigration that have swept Germany in recent years and as the country faces snap elections in February.

Of the people injured, 41 were severely hurt, the police in Magdeburg said. The authorities said that they believed the attack was deliberate, but that the driver acted alone.

The police searched an apartment in a town 25 miles south of Magdeburg where the doctor was reported to have lived and worked as a psychotherapist. The man first came to Germany in 2006, the authorities said.