BERLIN (AP) — A Tunisian man who was suspected of possible involvement in last week's Berlin truck attack has been released after investigators determined that he wasn't in contact with the main suspect immediately before the rampage, prosecutors said Thursday.

The 40-year-old was detained in Berlin on Wednesday. Federal prosecutors said at the time that his telephone number was saved in suspect Anis Amri's cellphone and that they suspected he may have been involved.

Prosecutors' spokeswoman Frauke Koehler said Thursday that investigators had suspected Amri might have sent him a message and a picture over a messenger service shortly before the Dec. 19 attack at a Christmas Market.

But "further investigations determined that the man who was provisionally detained isn't this possible contact person of Anis Amri, so he had to be released from custody," Koehler told reporters.

Amri is believed to have driven the truck that plowed into the market, killing 12 people. His fingerprints and wallet were found in the truck.

The Islamic State group has claimed responsibility for the attack. It also released a video showing Amri pledging allegiance to its leader, Abu Bakr al-Baghdadi.

Investigators have determined that the video is genuine, Koehler said.