The Tunisian man who killed 12 people last month by plowing a truck into a Berlin Christmas market had lived under at least 14 different names in Germany, a regional police chief said on Thursday, raising more questions about security lapses.

Anis Amri, shot dead by Italian police in Milan on Dec. 23, had been marked as a potential threat by authorities in the western federal state of North Rhine-Westphalia (NRW) in February 2016, some six months after he arrived in Germany and applied for asylum.

"He acted in a conspiratorial manner and used various personalities," Dieter Schuermann, head of the NRW Criminal Police Unit, told the regional parliament during a briefing.