Berlin: 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 at the foot of the Kaiser Wilhelm memorial church, one of west Berlin's most famous landmarks, at about 8pm 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."
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.
The attack fuelled 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 IS.
The mass influx of migrants and refugees to the European Union has deeply divided its 28 members and fuelled the rise of populist anti-immigration movements that hope to capitalise on public concerns next year in elections in France, Germany and the Netherlands.
Slovakia's Prime Minister Robert Fico said the latest attack would change perceptions of migration. "I think that the cup of patience is beginning to spill over and Europe's public will rightfully expect rather stronger measures," he said.
Nigel Farage of Britain's UK Independence Party tweeted: "Terrible news from Berlin but no surprise. Events like these will be the Merkel legacy."
On Tuesday morning, investigators removed the black truck from the site for forensic examination. People left flowers at the scene and notes, one of which read: "Keep on living, Berliners!" One woman was crying as she stopped by the flowers.
Bild newspaper cited security sources as saying the arrested man was Naved B. and had arrived in Germany a year ago. In legal cases German officials routinely withhold the full name of suspects, using only an initial.
A security source told Reuters the suspect had been staying at a refugee centre in the now defunct Tempelhof airport.
Die Welt said police special forces stormed a hangar at Tempelhof at around 4 a.m. (0300 GMT). A refugee there who gave his name only as Ahmed told Reuters security guards had told him there was a raid at around 4am.
Prosecutors declined to immediately comment on the report.
Merkel and de Maiziere both stressed the need for Germans to remain uncowed by the attack.
"We do not want to live paralysed by the fear of evil," said the chancellor, who discussed the attack by phone with US President Barack Obama and convened a meeting of her security cabinet.
"Even if it is difficult in these hours, we will find the strength for the life we want to live in Germany - free, together and open."
Other European countries said they were reviewing security.
Austrian Interior Minister Wolfgang Sobotka said he had told the heads of regional police forces to intensify surveillance measures. He called for biometric and fingerprint checks to be introduced along the Balkan route travelled by many migrants arriving in Europe, in order to better control foreign militants' movements.
London police said they were reviewing their plans for protecting public events over the festive period.
Flags will be hung at half-mast around Germany on Tuesday and Berlin Christmas markets were closed for the day out of respect. The German soccer league announced a minute's silence at all matches on Tuesday and Wednesday, at which players will wear black ribbons.
Dresden tourist information service said authorities had erected concrete blocks around the Striezelmarkt, one of Germany's oldest Christmas markets, to increase security.
Festive markets selling ornate, often hand-crafted decorations, seasonal foods and hot spiced wine are a beloved tradition in Germany.
Manfred Weber, head of the centre-right European People's Party, said: "It's not an attack on a country; it's an attack on our way of life, on the free society in which we are allowed to live."