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BERLIN, Germany (CBSMiami/AP) — Authorities in Germany have released a man suspected in Monday’s deadly truck crash in Berlin because there isn’t sufficient evidence to tie him to the rampage.

Twelve people were killed and dozens more were injured when the driver of a speeding tractor-trailer barreled into a crowded Christmas market.

ISIS is now claiming responsibility.

Law enforcement arrested a 23-year-old Pakistani migrant who arrived in Germany about a year ago and was living in a refugee center but federal prosecutors said Tuesday afternoon that the man denied involvement in the attack.

They noted that witnesses were able to follow the truck’s driver from the scene but lost track of him. The man arrested matched witness descriptions of the truck driver, but investigators haven’t been able to prove that he was in the truck’s cab at the time of the attack.

Under German law, prosecutors have until the end of the calendar day following an arrest to seek a formal arrest warrant keeping a suspect in custody.

Authorities have called the crash an intentional attack.

German chancellor Angela Merkel said terrorism must be assumed but Germans shouldn’t be paralyzed by fear. She’s been a strong supporter of accepting refugees in Germany.

Amateur video shows the chaotic aftermath of the crash as bystanders tended to the injured.

“I spoke to two people who were lying on the floor with broken limbs but they were going to be ok. I saw one guy being dragged away with blood on his face,” said British tourist and eyewitness Mike Fox.

Police are looking into whether the truck was hijacked from a Polish construction site.

Officials say the assailant shot and killed the truck’s driver, an unidentified Polish citizen who was found dead inside the vehicle.

Monday’s incident follows a similar attack in Nice, France in July when a truck mowed down revelers watching fireworks on Bastille Day killing 86 and injuring more than 200.  ISIS claimed responsibility for that attack.

In November, the U.S. State Department warned Americans traveling to Europe to “exercise caution at holiday festivals, events, and outdoor markets” after ISIS encouraged lone wolf attacks on soft targets.

Law enforcement officials have now stepped up security at Christmas markets in major U.S. cities.

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