BERLIN (AP) — A police official says that German authorities knew of 14 different identities used by Berlin Christmas market attacker Anis Amri.

Investigators say the 24-year-old Tunisian drove a truck into the market on Dec. 19, killing 12 people. He was killed Dec. 23 in a shootout with Italian police in a Milan suburb.

Amri came to Germany in mid-2015. Authorities later put him on a list of potentially violent Islamic extremists. Separately, he was investigated for receiving benefits simultaneously under two different identities.

The head of North Rhine-Westphalia state's criminal police, Dieter Schuermann, told regional lawmakers Thursday that authorities couldn't find evidence of possible attack plans that would stand up in court, news agency dpa reported. He said they "exhausted all legal powers to the limit to ward off potential dangers."