A man who drove a van into a crowd of people in the German city of Muenster on Saturday acted alone, according to police.
The driver killed two people and injured 20 others when he plowed into a restaurant's open terrace in an apparently deliberate act before fatally shooting himself.
The driver was a German citizen, said Herbert Reul, state minister for internal affairs in North Rhine-Westphalia.
There was no known connection to radical Islam, he said, but investigators are still combing through the man's background.
Authorities are looking into whether the driver had a history of mental illness.
Asked about a motive behind the attack, German Interior Minister Horst Seehofer said in a press conference Sunday that the man, who has not been named, could have been mentally ill.
"We continue investigating in all directions," Seehofer told reporters.
Muenster police spokesman Rolf Werenbeck-Ueding also told CNN that the driver had a history of petty crime.
Police had said they are investigating witness reports of people fleeing out of the van after the attack. Spokesman Jochan Laschki said the driver had no accomplices, and the investigation is ongoing.
The attack happened about 3:30 p.m local time in the old part of the western German city, an area popular on weekends. It was a warm sunny afternoon, one of the first nice days of spring, and many people were out, Bild editor Julian Reichelt told CNN.
German Chancellor Angela Merkel said she was "deeply shocked by the terrible events in Muenster."
In a statement tweeted by a German government spokeswoman, Merkel said "everything is now being done to clarify the act and support the victims and their families."
"With dismay, I learned of the terrible incident in Muenster," Seehofer said in a statement Saturday, adding, "Police in Muenster and throughout (the state of North Rhine-Westphalia) are now working hard to investigate the matter."
Federal authorities are in close contact with local officials, Seehofer said.
Muenster, with about 300,000 people, is home to numerous universities and has a student population of about 58,000, the city government says. The city calls itself the cycling capital of Germany and says about 100,000 residents use a bike daily.
Saturday's crash occurred on the one-year anniversary of a similar attack in Stockholm, Sweden, when a stolen beer truck struck pedestrians, killing five people.
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