BERLIN — German officials Tuesday released the chief suspect in the gruesome terrorist attack against a Christmas market in Berlin, launching a nationwide search for an attacker that the Islamic State claimed had acted on the terrorist group’s behalf.
Early in the day, the authorities announced that they had the arrested a 23-year-old Pakistani asylum seeker who arrived in Germany last December. But as the day progressed they expressed uncertainty that he was indeed the driver of the truck.
By evening the federal prosecutor said the man had been released because there was no proof linking him to the crime. An examination of both the suspect and the cab of the truck turned up no proof that he had been in it, the prosecutor said.
That meant the culprit was still on the run, and far-right politicians wasted no time in pinning responsibility for the deaths on Chancellor Angela Merkel.
The attack ushered in the shattering realization that Germany, too, was now among the front ranks of European countries, alongside France and Belgium, that have suffered large-scale attacks in recent years.
The Islamic State released a statement Tuesday through its Amaq news agency describing the driver of the truck as “a soldier” who had answered the call to wage attacks against countries fighting the group. But it offered no other details about the driver’s identity or whether he had directly interacted with the group or was just sympathetic to it.
The attack in Berlin, which killed 12 people and wounded many others, immediately heightened the sense of political vulnerability around Merkel, a linchpin of European unity. And it came at a precarious time of concern about Russian meddling and a populist backlash over her decision to open German borders to nearly a million migrants and refugees in 2015.
Her political opposition issued a surprisingly speedy and stinging reproach, even in the midst of the grieving over the 12 killed and dozens wounded Monday when a driver plowed the truck through Christmas stalls selling holiday gifts, crafts and snacks, and then fled.
The Berlin victims were labeled “Merkel’s dead” by Marcus Pretzell, leader of the Alternative for Germany party in the country’s most populous state, North Rhine Westphalia. Frauke Petry, the party leader, said bluntly, “Germany is no longer safe.”
Daniela Schwarzer, leader of the German Council on Foreign Relations, said that the statements offered a taste of the bitter debate to come in 2017.
“They were very quick to link this directly to Merkel, and they said horrific things, blaming her for the deaths,” Schwarzer said.
“That gives us a sense of what is coming in the electoral campaign,” she said, adding that after an especially nasty presidential campaign in the United States, German politicians, too, may abandon traditional decorum.
Early in the day, a somber Merkel, dressed in black, acknowledged what people across Europe had been fearing with the approach of the holiday season: One of the Continent’s ubiquitous Christmas markets appeared to have been targeted for assault.
“We must assume at the current time that it was a terrorist attack,” Merkel told reporters Tuesday.
She later appeared in a black wool coat, bearing a white rose to lay at a memorial outside of a church in the heart of western Berlin, near the scene of the attack.
Even as she was mourning, Peter Frank, the country’s federal prosecutor, insisted that while the similarities to last summer’s Bastille Day attack in Nice, France, led his office to suspect that the Berlin attack was motivated by terrorism, he was unable to produce any hard evidence.
“We are investigating in all directions,” Frank said, explaining that he decided to start an investigation given the symbolism of the target and the timing, less than a week before Christmas Eve.
“We have not limited ourselves to one suspect or one possible perpetrator,” he added, “But we can’t make a final assessment whether it is a terrorism-motivated attack, or whether it was a copycat act.”
What authorities can say for certain is that a tractor-trailer with Polish license plates and laden with steel rods jumped a sidewalk around 8 p.m. Monday and plowed into the market near the Kaiser Wilhelm Memorial Church, a symbolic Berlin site whose spire, jagged from bomb damage, was intentionally left unrepaired after World War II.
A man believed to be the driver fled after the attack and another man, identified as a Pole, was found dead with gunshot and stab wounds in the passenger seat, police said.
Less than an hour later, a man who Berlin police said was seen fleeing the scene was arrested nearby on suspicion of involvement. He was the Pakistani man later freed.
Officials in Berlin have been straining to deal with a flood of asylum applications. Although the number of arrivals has slowed recently from a high point in the summer of 2015, tens of thousands remain in communal housing, awaiting processing of their applications.
In addition to the 12 dead, 48 people were wounded at the Berlin market, 18 of them critically, said Thomas de Maizière, Germany’s interior minister.
De Maizière said there would be increased security in public places and at key transit hubs, and that local officials would make decisions about events that might need to be curtailed for safety reasons.
Officials have been aware for some time of the risk of attacks on holiday-themed events in Europe.
The State Department issued a travel alert on Nov. 21 recommending that Americans “exercise caution at holiday festivals, events, and outdoor markets” throughout the Continent.
“Credible information” indicated that the Islamic State, its affiliates and sympathizers “continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events,” the alert said, and that an attack could come with little or no warning.