Officials also knew Amri was tightly linked to Germany's radical Islamist network and had looked up instructions online to build pipe bombs, the Süddeutsche Zeitung daily reported.
The latest version of their file on Amri, which included information on his eight different identities, was updated on December 14th - just five days before he rammed a truck into a crowded Christmas market in Berlin.
Düsseldorf police deemed him a Salafist and radical fundamentalist, while Dortmund police had rated him a sympathiser of the Islamic State group.
Amri had been a regular guest at a religious school in a Dortmund apartment run by a notorious radical known as Boban S. that was believed to be a recruitment ground for jihadists.
Nevertheless, on an eight-point scale assessing an individual's potential danger, with "one" the highest threat, counter-terrorism experts rated him a "five" - meaning they considered an attack possible but unlikely.
Shortly after the Christmas market rampage, authorities admitted that counter-terrorism services had been watching Amri, suspecting he may have been plotting an attack.
But surveillance was dropped in September, as police thought he was primarily as a small-time drug dealer.
Chancellor Angela Merkel ordered a sweeping review of the security apparatus after the attack, so that any necessary reforms could be agreed and implemented quickly.