Anis Amri, 24, was also learning how to make bombs and was barred from flying to America because of his links to ISIS, US officials have revealed.
Amri, who had six aliases and three fake passports, also has an array different Facebook accounts including one where his profile picture was a lion - a key motif used by jihadists to symbolise honour.
It contains a single video of him filming himself in the centre of Berlin in September - with German media claiming it could have been a reconnaissance video.
Wire taps revealed that two months ago Amri had told a hate preacher that he was willing to blow himself up - and had also inquired about buying automatic weapons from a police informant.
But German officers still did not believe they had enough evidence to arrest him, according to Spiegel.
Police today revealed that his fingerprints were found on the door of the hijacked lorry used to murder 12 people at a Christmas market in Berlin on Monday night.
Officers have been carrying out raids across Germany as the international manhunt continued for the failed Tunisian asylum seeker with German police under fire for a string of blunders that let him go free.
Four men were arrested in Dortmund - where Amri once lived with a hate preacher. The men have reportedly had close contact with him in recent months.
A flat was also raided in Berlin, but was empty, and a shelter for asylum seekers was searched in Emmerich, eastern Germany, where one man was questioned.