German police are looking for an asylum-seeker from Tunisia after finding an identity document under the driver's seat of a truck that plowed into a Berlin Christmas market and killed 12 people, officials and security sources said on Wednesday.
The federal prosecutor's office offered a reward of up to 100,000 euros ($104,000) for information leading to the capture of the suspect, whom it identified as 24-year-old Anis Amri.
"Beware: He could be violent and armed!" the prosecutor's office said in a statement, in which it described Amri as 1.78 meters (5'8") tall, with black hair and brown eyes.
German police commandos raided two apartments in the Berlin district of Kreuzberg late on Wednesday but did not find Amri, Die Welt newspaper reported, citing investigators.
Amri's father and security sources told Tunisia's Radio Mosaique that he had left Tunisia seven years ago as an illegal immigrant and had spent time in prison in Italy.
In Duesseldorf, Ralf Jaeger, interior minister of the western state of North Rhine-Westphalia (NRW), said the Tunisian appeared to have arrived in Germany in July 2015 and his asylum application had been rejected.
He seemed to have used different names and had been identified by security agencies as being in contact with an Islamist network. He had mainly lived in Berlin since February, but was recently in NRW, Jaeger added.
After being turned down for asylum, the man should have been deported but could not be returned to Tunisia because his documents were missing, he said.
"Tunisia at first denied that this person was its citizen," said Jaeger, adding that German authorities started the process of getting new identity papers in August 2016. "The papers weren't issued for a long time. They arrived today."
A judicial source told Reuters that German authorities had observed Amri over a period this year to try to determine whether he had planned a robbery to fund the purchase of automatic weapons for a possible attack with accomplices.
Authorities stopped their monitoring activities because they could not prove their suspicions, the source said.
The new details have added to a growing list of questions about whether security forces missed opportunities to prevent the attack, in which a 25-tonne truck mowed down shoppers and smashed through wooden huts selling gifts, mulled wine and sausages in the deadliest attack on German soil since 1980.
Christmas markets have been a known potential target for Islamist militants since at least 2000, when authorities thwarted a plot to attack one in Strasbourg, France. And the modus operandi in Berlin was identical to that of a Bastille Day attack in the French city of Nice in July, when a Tunisian-born man rammed a lorry through a seaside crowd and killed 86 people.
The market at the scene of Monday's attack, at the foot of the Kaiser Wilhelm memorial church, stayed shut on Wednesday, but more than 60 other Christmas markets across the German capital re-opened under tightened security.
"We don't want to let the terrorists win. If everyone stays away, they are winning," said tourist Nicki Anning at the Gendarmenmarkt Square in central Berlin.
Berlin authorities said 12 people seriously injured in Monday's attack were still being treated in hospital.
The pre-Christmas carnage at a symbolic site - under the ruined spire of a church bombed in World War Two - has shocked Germans and prompted security reviews across Europe, already on high alert after attacks this year in Belgium and France.
The possible - though unproven - involvement of a migrant or refugee has revived a bitter debate about security and immigration, with Chancellor Angela Merkel facing calls to clamp down after allowing more than a million newcomers into Germany in the past two years.
Merkel, who will run for a fourth term next year, has said it would be particularly repugnant if a refugee seeking protection in Germany was the perpetrator.
U.S. President-elect Donald Trump condemned the Berlin attack on Wednesday, blaming "Islamist terrorists (who) continually slaughter Christians in their communities and places of worship as part of their global jihad".
"It's an attack on humanity and it's gotta be stopped," he told reporters in Palm Beach, Florida.
Police initially arrested a Pakistani asylum-seeker near the scene, but released him without charge on Tuesday.
The Polish driver of the hijacked truck was found shot dead in the cabin of the vehicle. Bild newspaper said he had been alive until the attack took place. It also quoted an investigator as saying there must have been a struggle with the attacker, who may have been injured.
Islamic State has claimed responsibility, as it did for the Nice attack.
The Passauer Neue Presse newspaper quoted the head of the group of interior ministers from Germany's 16 federal states, Klaus Bouillon, as saying tougher security measures were needed.
"We want to raise the police presence and strengthen the protection of Christmas markets. We will have more patrols. Officers will have machine guns. We want to make access to markets more difficult, with vehicles parked across them," Bouillon told the paper.
Bavarian Interior Minister Joachim Herrmann told German radio there was a higher risk of Islamist attacks because of the influx of migrants in the past two years, many of whom have fled conflicts in countries such as Syria, Iraq and Afghanistan.
The task of tracking the suspects and the movements of the truck may be complicated by the relative scarcity of security cameras in public places in Germany, compared with countries such as Britain.
The German cabinet on Wednesday approved a draft law to broaden video surveillance in public and commercial areas, a measure agreed by political parties last month after violent attacks and sexual assaults on women.
State surveillance is a sensitive issue in Germany because of extensive snooping by the Stasi secret police in Communist East Germany and by the Gestapo in the Nazi era.