German police have released a 40-year-old Tunisian man who had been a suspected accomplice of the Berlin Christmas market assailant.
"Further investigations indicated that he could have been involved in the attack", said prosecutors.
Authorities were driven to his arrest after his phone number was found on Amri's cell phone directory.
The suspect was taken into custody after officers searched his home and workplace.
"We are still in the middle of the work-up and we have to look at all the details carefully, only then can we make a final evaluation", said BAMF president Weise, adding, "The case of Amri is an occasion to re-examine some processes in our house".
Amri was being investigated for receiving asylum-seeker benefits in two different towns, under different identities, for a few days in late 2015. Amri had no phone with him in Milan, only the loose SIM card.
Wim de Bruin, spokesman for the Dutch public prosecution service told AFP: "We believe he was in Nijmegen, most likely last Wednesday".
Meanwhile Dutch lawmakers including anti-Islam politician Geert Wilders demanded an explanation over reports that Amri may have travelled through the Netherlands. In Milan, police killed him after he pulled a gun on them during a routine check.
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"In the Turin train station after arriving in France, he was shot twice cameras, while he was searching for information about trains that headed to Rome or Milan", wrote the Italian newspaper.
The man had been arrested on Wednesday in the Tempelhof district of the city, as the police investigation whether Amri had any accomplices in planning the attack and subsequently fleeing Berlin.
German magazine Focus quoted unnamed security sources as saying Amri had been texting messages and sending photos to "Islamist friends" only 10 minutes before the attack.
Kohler also said that the truck, which was used to drive into crowds at the Christmas market, had stopped after 60-80 meters thanks to its emergency brake system.
Amri was known to Tunisian police as a juvenile delinquent who drank and took drugs.
Denmark's domestic intelligence agency, PET, estimates that about 135 people have left the country to enter embattled Syria. There he spent four years in prison for starting a fire in a refugee centre, during which time he was apparently radicalised.
His journey across Europe has prompted fears that open borders in Europe's Schengen zone are being exploited by Islamic State. He was not named by German authorities.