A man detained after the Berlin Christmas market truck attack has been released due to lack of evidence, Germany’s chief federal prosecutor office said Tuesday, according to Reuters.

The 23-year-old Pakistani man was arrested shortly after the attack Monday, which left 12 dead and dozens more injured after a truck plowed into a crowd of people. 

German officials from the beginning stated that they were uncertain if the man was tied to the attack. 

{mosads}Authorities say the tractor-trailer had Polish license plates. A man, believed to be the driver, fled after the attack, while a Polish man was found dead in the passenger seat. The release of the Pakistani man, who had previously applied for asylum in Germany, suggests that the attack’s perpetrator could be still be at large.

German Chancellor Angela Merkel said the attack will be investigated as an act of terrorism. 

“We must assume at the current time that it was a terrorist attack,” Merkel said Tuesday.