The only person detained after Monday's attack against a Christmas market in Berlin has been freed from custody due to lack of evidence.

On Tuesday, the man authorities arrested for allegedly killing a dozen people by plowing through crowds in a busy Berlin Christmas market has been released, according the Chief Federal Prosecutor Office.

The prosecutor's office said the investigation "did not yield any urgent suspicion" against the man authorities thought was part of a possible terror attack. The suspect denied all liability for Monday's tragedy, according to Tuesday's police hearing.

Authorities lacked sufficient evidence to prove the man was sitting in the truck at the time of the attack.

Germany's police are on "high alert" in their pursuit of the armed-culprit, who is "still at large."

​On Monday, a semi-truck mowed down crowds at a holiday market festival, killing 12 people while injuring 48 more. Police said on Tuesday that 24 of those wounded in the attack returned from the hospital to their families.

Authorities remain adamant that the tragedy was an attack but express uncertainty of the perpetrator's motives, the German Interior Minister said Tuesday. German police recommended local citizens stay vigilant and report any suspicious activities to the proper authorities.