The police have recent released the suspect they had taken in, claiming that he was mistakenly arrested. In the chaos and confusion of the aftermath, it is not impossible that the police could make a mistake. It is better that they admitted their mistake early, so that the investigation can continue and the real perpetrator can be caught.
The man originally arrested was reported to be a 23-year-old Pakistani asylum seeker who arrived in Germany last year. Security sources told local media he was not previously known to intelligence agencies as a potential Islamist. According to German news agency dpa, blood-smeared clothing was found in the lorry, but no clothing stained with blood was found on the suspect. Also, when the 23-year-old was arrested he is not thought to have had a weapon with him.
German police released the man they arrested, claiming that there was not enough evidence to justify holding him. The man they arrested was an asylum seeker from Pakistan with no known connections to the Islamic State. It's likely that the truck attack on the Christmas market was carried out by Islamist terrorists.
The German police were in a hurry to arrest someone after the attack at the Christmas market. They want to show the public that people are safe. In their haste, they arrested the wrong person. They came out quickly and admitted their mistake. They also said that the person was still on the loose.