Spiegel Online has a pretty interesting interview (German only) with the former landlord of Anis Amri; police considers the landlord an important witness in investigations in the case.

According to him, while Amri carried an inner radicalized persona, he did live pretty modern and westernized; police that had him under surveillance at the time similarly indicated a conflict in this regard - Amri had contacts to salafists and radical mosques, but on the other hand worked as a small-time drug dealer becoming involved in turf fights who lived it up going to dance clubs at night, doing alcohol, XTC and cocaine and being pretty concerned about his looks. He showed his radical side occasionally. The landlord tells a story about a Libyan flatmate - an army officer in Germany for medical treatment - who'd loudly complain about IS in his home country; Amri got into a fight with him over that, calling him an infidel. Overall he got along with the others in the flat amicably though, if a bit chaotic at chores and such; the landlord - a former Tunisian police officer who had moved to Germany with his German wife 25 years ago and worked as a professional truck driver since then* - and Amri occassionally liked to talk shop about trucks, with Amri telling him he learned how to drive one from his brother (Amri stole a truck in Tunisia at age 18, which he obviously didn't tell him). The final radicalization of Amri only occured during the last two weeks before the attack, with him noticably withdrawing to his room to read the Qu'ran. This led to increasing discomfort for the landlord and the flatmates, with the landlord getting rid of him mid-december.

Amri last visited the flat on December 19th; apologizing to the Libyan guy "if he had felt insulted by him" as well as the landlord for "any problems during his tenancy" and then packing up the last of his belongings still in the flat. Into the same backpack found in the truck at the christmas market four hours later.

* small caveat in this regard: The landlord himself has been investigated for possible courier services for a common acquaintance of him and Amri, although the exact items moved can not be qualified. Said acquaintance - Bilel B.A. - last met Amri the day before the attack, eating out with him in a restaurant; while investigations against Bilel B.A. were dropped for lack of evidence of any wrongdoing, he has still been deported to Tunisia since then.