KARLSRUHE, GERMANY (REUTERS) - German authorities have released a Tunisian man detained on suspicion of involvement in the truck attack on a Berlin Christmas market last week that killed 12 people, a spokeswoman for the federal prosecutor's office said on Thursday (Dec 29).

"Further investigation has shown that the arrested person was not the possible contact person of Anis Amri and therefore he was released," Frauke Koehler said, referring to the man believed to have hijacked the truck and ploughed it into crowds at a Christmas market in the capital last week.

Investigators found the mobile phone number of the released 40-year-old Tunisian stored in the phone of Amri.

The spokeswoman said that a gun Amri used in the truck had the same caliber as the one he fired at Italian police in Milan, where he was shot dead last week. More tests were needed to determine whether it was the same gun.

She added that the truck's automatic breaking system stopped the vehicle 70m to 80m after it hit the market, avoiding more casualties.