Berlin Christmas attack
© Fabrizio Bensch / ReutersPolicemen investigate the scene where a truck ploughed into a crowded Christmas market in the German capital last night in Berlin, Germany, December 20, 2016.
German police have detained an acquaintance of the alleged Berlin attacker Anis Amri during a raid at a refugee facility, the federal prosecutor's office announced. The detained man is said to have dined with Amri on the eve of December 19 attack.

The attacker's suspected accomplice, a 26-year old Tunisian man, was snatched during a police operation at a refugee facility in Berlin-Spandau, Frauke Kohler, spokeswoman for the Federal prosecutors office confirmed on Thursday.

"According to the current findings, the suspect and Anis Amri knew each other since around late 2015," Johler said.

"In the course of our investigations we found out that the two had met on the eve of the attack in a restaurant in Berlin-Mitte," and were involved in an "intense discussion," the official said.

"This resulted in [our] allegation that the suspect, the 26-year-old Tunisian, could have been possibly involved in the [terrorist] act, or at least could have known about the plan of the assault."

Members of the German Federal criminal police (BKA) who raided the refugee facility where the 26-year old Tunisian had a room, also seized "communication devices."

"They [devices] are being evaluated right now," Kohler said. She stressed though, that the information gathered by the Federal prosecutor's office so far, was not enough to keep the suspect in detention.

Nevertheless, a temporary detention order currently in place, has been ordered by a judge on request of the Berlin prosecutor's office. This is however not over a terrorist-related issue, but rather of alleged social-system fraud, Kohler said, as cited by Die Welt.

Police also searched a room of Amri's ex-flatmate in Berlin on Wednesday, a statement by the Federal Prosecutor's office said. The respective person (name not disclosed) is now "considered a witness," by the authorities.

"The analysis of Amri's mobile phone showed that he had tried to reach the "witness" on the morning and afternoon of the day of the attack," the statement says. Yet, according to the officials its still not clear whether they in fact had a conversation.

Investigators have seized "communication devices" of the "witness" and are now analyzing the equipment. After killing a polish driver and stealing his lorry, Anis Amri, allegedly ploughed the vehicle into a Christmas market in central Berlin on December 19, killing 12 people.

Four days later, Amri, a Tunisian refugee who arrived in Germany in 2015, was shot dead by police in Milan after fleeing to Italy, allegedly via France and the Netherlands.

On Thursday, Italian authorities confirmed that the gun, which Amti used in a shootout with police in Milan, was the same one used to kill the Polish driver.