German Authorities Detain Tunisian Man Suspected of Helping Alleged Berlin Attacker German prosecutors said the man could have been involved in the Berlin attack.

 -- German authorities have detained a 40-year-old Tunisian man who “could have been involved in the attack” on a Christmas market in Berlin, Germany’s federal prosecutor said today in a statement.

The Federal Prosecutor’s Office did not name the man but described him as a “contact person” for the alleged attacker, Anis Amri, who was shot dead by police in Milan last week. Amri, a 24-year-old Tunisian national, had the older man’s phone number stored in his cellphone, according to the statement.

Investigators are working to determine what role, if any, the unnamed Tunisian man played in the Dec. 19 attack on the Christmas market at Breitscheidplatz, a public square in the heart of Germany’s capital. Authorities searched the man’s offices today, according to the prosecutor’s statement.

Officials have identified Amri as the likely assailant in the deadly attack, citing evidence discovered at the crime scene, including fingerprints in the cab of the truck that was used to plow through the busy marketplace. At least 12 people were killed, and dozens more were injured, according to German authorities.

Berlin police spokesman Winfried Wenzel told ABC News on Saturday that Amri’s mobile phone, wallet and ID were discovered in the cab of the truck. The truck was stolen in Poland from a building site, and its driver, a Polish citizen, was found dead with gunshot wounds in the back of the vehicle. The spokesman said authorities believe a violent struggle took place in the cab at some point around the time of the attack.

ISIS claimed responsibility for the assault, calling Amri “a soldier of the Islamic State” in a statement released by the terrorist group.

In a video posted on social media that appears to have been recorded before the attack, Amri pledges allegiance to ISIS and says he is avenging the bombing of Muslims, urging others around the world to take up jihad.

“My message to the crusaders who bombard Muslims every day: With God’s will, I swear we’re coming to slaughter you, you pigs,” Amri says in the recording. “I encourage all my Muslim brothers in every place to conduct jihad in the name of the religion.”

Ralf Jaeger, the interior minister of the German state of North Rhine–Westphalia, told reporters last week that Amri had known ties to the local radical Islamic scene and had been deemed a threat by several security agencies.

Authorities are still trying to piece together Amri’s movements after the attack. According to Italian police, he is believed to have traveled through France before arriving on a train at Milan’s central railway station at approximately 1 a.m. local time last Friday. Approximately two hours later, near a train station in the Sesto San Giovanni area in suburban Milan, Amri was approached by two police officers who wished to conduct a routine identity check. The officers were unaware he was the man at the center of the Europe-wide manhunt.

“He was a man from northern Africa, like there are many in the Milan area, and ours was a routine check that was carried out by two young and good police officers,” Milan Police Chief Antonio de Iesu said at a press conference on Friday.

Sesto San Giovanni Police Chief Roberto Guida told reporters that Amri initially appeared calm while emptying his pockets and satchel. Then he suddenly pulled out a loaded weapon fired once at the chief patrol officer, who was closer to him, before fleeing behind a nearby car. The other officer flanked Amri and shot him dead, Guida said.

The wounded police officer was taken to a local hospital, where he is recovering, according to Italy’s Interior Ministry.

Italian authorities confirmed the man killed was Amri, using fingerprints provided by German authorities, according to German’s Federal Prosecutor Peter Frank.

Today, Italian police released an image that they say shows Amri at a train station in Turin on Dec. 22 at 10:14 p.m. local time.

On Saturday, Tunisian authorities arrested three men in connection with the attack in Berlin. Among those arrested was Amri’s nephew, who admitted to using an encrypted chat application to communicate with his uncle, according to Tunisia’s Interior Ministry.

Amri allegedly encouraged his nephew — his sister’s son — to adopt jihadist ideologies and urged him to pledge allegiance to ISIS. Amri even sent his nephew money so he could travel to Germany and join the group, according to Tunisia’s Interior Ministry.

“As he was interrogated, he confessed that he communicates with his uncle through the application Telegram to evade security surveillance using its encryption and secrecy,” the ministry said in a statement on its website.

Amri’s nephew was not named in the statement, and the identities of the other two men arrested are unknown; the three men — whom the ministry said were a terrorist cell — are 18 to 27 years old.

ABC News’ Paul Blake, Molly Hunter, Matthew McGarry, Rym Momtaz, Phoebe Natanson, Bruno Nota, Kirit Radia and Ben Gittleson contributed to this report.