BERLIN -- An asylum seeker detained by police after a large truck was rammed into a Christmas market in Berlin might not have been the driver, Berlin police said.
Berlin police president Klaus Kandt said officials could not be certain the man, who was picked up about a mile away from where 12 people were killed and 48 others injured on Monday evening, was the attacker.
Moments before he spoke, German Interior Minister Thomas De Maiziere said the suspect was "probably from Pakistan" and that he had denied any involvement in the incident.
German authorities are investigating the incident as a terror attack.
De Maiziere said the man in custody had entered Germany on Dec. 31, 2015, and sought asylum in Germany, but that his application had not been completed.
Intelligence and police sources earlier said the man detained had arrived to the country in Passau, a city on Germany's border with Austria, after traveling through the Balkans.
Berlin police said the truck, owned by a Polish company, "was steered deliberately into the crowd." It was carrying 25 tons of steel at the time, the vehicle's owner said.
The suspect in custody was detained by police just more than a mile from the scene. Another man was found dead in the passenger seat of the truck.
Ariel Zurawski, owner of the truck company, told TVN 24 the vehicle might have been hijacked, as his cousin -- the truck's regular driver -- couldn't have been behind the wheel.
Berlin police corroborated the information, saying the man found dead was a Polish citizen and was not at the wheel during the incident.
De Maiziere said the man found in the truck appeared to have been shot dead, but that authorities had not found the weapon used.
The minister called for Christmas markets to be closed for a day of mourning.
"But to cancel them would be wrong," he said, adding they would hopefully reopen Wednesday.
Merkel: 'Hard to bear'
German Chancellor Angela Merkel said it would be "especially disgusting" if the suspect had been given asylum.
Dressed in black and making her first public comments on the attack late Tuesday morning, she called for unity in the country.
"I know that it would be especially hard to bear for us if it was to be confirmed that a person (who) committed this act ... was given protection and asylum in Germany," Merkel said.
"This is a very difficult day. I, like millions of people in Germany, am horrified and deeply sad about what happened yesterday in Berlin."
Monday's attack could cause further political upheaval for Merkel, who has come under criticism over her government's generous acceptance of refugees.
Germany has taken in more than 890,000 asylum seekers in the past year, a marked difference to other European nations.
But a backlash has been growing, fueled in part by Islamist terror attacks in Germany and across the continent.
This month, Merkel called for the ban on Muslim full-face veils, in a concession to the right, anti-immigrant wing of her Christian Democratic Union party.