A Pakistani asylum-seeker arrested on suspicion of killing 12 people by mowing through a Berlin Christmas market in a truck may not be the attacker, and the real perpetrator could still be on the run, German police said on Tuesday.
The truck smashed into wooden huts serving mulled wine and sausages at the foot of the Kaiser Wilhelm memorial church, one of west Berlin's most famous landmarks, at about 8 p.m. on Monday. Forty-eight people were injured, 18 severely.
News of the arrest of the 23-year-old Pakistani led politicians in Germany and beyond to demand a crackdown on immigration.
Chancellor Angela Merkel told reporters: "There is much we still do not know with sufficient certainty but we must, as things stand now, assume it was a terrorist attack."
RELATED: Scenes from the Berlin Christmas market attack
She added: "I know it would be especially hard for us all to bear if it were confirmed that the person who committed this act was someone who sought protection and asylum."
In a dramatic twist, police later said the suspect had denied the offence and might not be the right man.
"According to my information it's uncertain whether he was really the driver," Police President Klaus Kandt told a news conference.
Berlin police tweeted that they were "particularly alert" because of the denial. "Please be alert," they added.
Die Welt newspaper quoted an unnamed police chief as saying:
"We have the wrong man. And therefore a new situation. The true perpetrator is still armed, at large and can cause fresh damage."
The truck belonged to a Polish freight company and its rightful driver was found dead in the vehicle. Interior Minister Thomas de Maiziere said a pistol believed to have been used to kill him had not yet been found.
German media said the arrested man had jumped out of the driver's cab and run down the street towards the Tiergarten, a vast park in central Berlin. Several witnesses called police, including one who chased the suspect while on the phone, constantly updating officials on his whereabouts.
"STATE OF WAR"
The attack fueled immediate demands for a change to Merkel's immigration policies, under which more than a million people fleeing conflict and poverty in the Middle East, Africa and elsewhere have arrived in Germany this year and last.
"We must say that we are in a state of war, although some people, who always only want to see good, do not want to see this," said Klaus Bouillon, interior minister of the state of Saarland and a member of Merkel's Christian Democrats (CDU).
Horst Seehofer, leader of the CDU's Bavarian sister party, said: "We owe it to the victims, to those affected and to the whole population to rethink our immigration and security policy and to change it."
The record influx has hit Merkel's ratings as she prepares to run for a fourth term next year, and boosted support for the anti-immigrant Alternative for Germany (AfD). Senior AfD member Marcus Pretzell blamed Merkel for the attack on Twitter.
AfD leader Frauke Petry said Germany was no longer safe and "radical Islamic terrorism has struck in the heart of Germany."
The incident evoked memories of an attack in Nice, France in July when a Tunisian-born man drove a 19-tonne truck along the beach front, mowing down people who had gathered to watch the fireworks on Bastille Day, killing 86 people. That was claimed by Islamic State.