BERLIN, Dec. 20 (UPI) -- German authorities said Tuesday they've released a man initially suspected in the truck crash that killed 12 people at a holiday market in Berlin -- an event officials are investigating as an act of terrorism.
Berlin police said their investigation has determined a 23-year-old Pakistani asylum-seeker they arrested appears to be above suspicion -- based partly on the fact that he had no blood on his clothing at the time of his arrest, shortly after the crash. He was detained leaving the scene.
Police said the driver of the delivery truck almost certainly would have had blood on his clothing, because it was everywhere inside the truck's cab.
"The investigations so far did not result in an urgent grounds for suspicion," prosecutors said in a statement. "The criminal investigations carried out so far have not been able to prove a presence of the accused during the incident in the truck."
Officials said the driver is likely still at large, and they continue to acknowledge the possibility that the event was carried out by a migrant.
The stolen truck, loaded with steel beams and belonging to a Polish company, drove through a festive holiday market in Berlin's west flank on Monday. At least 48 people were injured, 18 seriously.
The company that owned the truck said it lost contact with its driver prior to the attack, leading police to suspect it had been hijacked somewhere along its route.
German Chancellor Angela Merkel on Tuesday said the incident is being treated by police as a terrorist attack.
"I know it would be especially hard to bear for all of us if it should be confirmed that the person who committed this act sought protection and asylum in Germany," she said. "This would be especially despicable toward the many, many Germans who are daily engaged in helping refugees, and toward the many, many people who truly need this protection and strive to integrate themselves into our country."
"The executor of the operation in Berlin is a soldier of the Islamic State and he executed the operation in response to calls to target nationals of the coalition countries," the statement said.
Authorities will likely be at least somewhat skeptical of the claim, however, as the terror group has previously demonstrated its willingness to take responsibility for acts of violence in which it is not directly involved.
The group claimed credit for a knife attack in October that killed a teenage boy. Investigators doubted the claim, though, saying it didn't align with evidence in the case.
German authorities still aren't sure yet whether Monday's crash was a deliberate act.
While the number of refugees entering Germany dropped in 2016, Merkel's open-door policy has polarized voters. The Berlin incident threatens to undermine her domestic policy as Germany heads to an election year, and could lead to more support for the anti-immigrant Alternative for Germany Party, known as AfD.
"Germany is no longer safe," AfD co-chairwoman Frauke Petry said. "We must be under no illusions. The breeding ground in which such acts can flourish has been negligently and systematically imported over the past year and a half."
Monday's crash has similarities to a July attack in Nice, France, in which a truck plowed through a crowd, killing 80. The Islamic State also took credit for that attack.