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NEW YORK (CBSMiami/AP) — The search is intensifying across Europe for the driver who mowed down dozens of people at a Berlin Christmas Market.

Police are concerned he is still a threat. Anis Amri is a young Tunisian whose ID, and asylum papers, were found in the cab of the truck that plowed through a Christmas Market in Berlin Monday. Amri reportedly used six different aliases.

A German lawmaker said Amri has ties to Islamic extremists and was supposed to be deported from Germany earlier this year. ISIS has claimed it inspired the attack.

Twelve people were killed in the rampage including the truck’s original driver, Lukasz Urban, who was found shot and stabbed in the cab.

The truck’s GPS system indicates that by 3:45 p.m. on Monday Urban was probably not in control of the truck, that it was being driven as if the person inside was ‘learning to drive’. Just before 5pm, the engine was left running for 45 minutes, but the truck did not move.

Then at 7:40pm it started towards the Christmas Market.

While authorities are stepping up security measures around Germany, critics of the country’s refugee program say it was only a matter of time until an attack like this took place.

The Berlin market, like other attack sites in Europe this year, has become a place for people to come together. Dozens of refugees and Germans gathered Wednesday near the crash site to sing in solidarity.

Other Christmas markets around Berlin, which had closed because of the attack, have begun to re-open.