Investigators across Europe are trying to determine whether Anis Amri, a failed asylum seeker from Tunisia who was shot dead by police in Milan on Friday after killing 12 people in Berlin in the name of Islamic State, had any accomplices.

A spokeswoman for Germany’s Federal Prosecutor’s Office said the Tunisian man had been detained on Wednesday on suspicion Amri may have sent him a voice message and picture shortly before the attack.

“Further investigation has shown that the arrested person was not the possible contact person of Anis Amri and therefore he was released,” Frauke Koehler told reporters in Karlsruhe.

Investigators had found the mobile phone number of the released 40-year-old Tunisian stored in Amri’s phone. His home and business premises were raided. He was not named.

Koehler said a video circulated on the Internet after the attack showing Amri at a bridge in Berlin swearing allegiance to Islamic State and urging Muslims to carry out more attacks was authentic.

Amri arrived in Europe by boat to the Italian island of Lampedusa in 2011 and travelled to Germany last year where he was facing deportation after his asylum application was rejected.