German prosecutors have identified 32-year-old Meher D., a Tunisian-born "Islamic State" (IS) member, as the key accomplice to the Berlin truck attacker Anis Amri. The suspect apparently communicated with Amri online and provided instructions before and after the December 2016 attack.

The Federal Court of Justice issued an international arrest warrant for Meher D., according to Friday reports published by Germany's public broadcasters NDR and WDR, as well the Süddeutsche Zeitung newspaper. Authorities reportedly believe the IS member is located in Libya.

Read more: German government accused of blocking Anis Amri investigation

When asked about the reports, however, German prosecutors refused to either confirm or deny the existence of the warrant.

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Tunisian national Anis Amri, who was 23 at the time, stole a truck and drove it into a Christmas market in Berlin, killing 12 people and injuring 48 more in 2016. He then fled the scene and was shot by Italian police near Milan four days later.

After taking possession of his phone, police noticed a Telegram message that arrived hours after his death, in which a user dubbed moumou1 was asking if Amri was alright.

German investigators soon found other messages from the same person on the phone. According to them, the user encouraged Amri to commit an attack and apparently served as a mentor to the man, even sending Amri a document listing arguments to justify killing women and children in "acts of martyrdom."

A notable exchange took place on December 19, 2016, while Amri was heading to the site of the attack in Berlin Breitscheidplatz in the stolen truck. In an audio message, Amri says: "I'm in the car now," with moumou1 one replying "Thank God."

Read more: How terror suspect Anis Amri eluded German authorities

Another mentor for Cologne ricin suspect?

Separately, German authorities also tracked down a payment of €700 ($818) that Amri had sent to a Tunisian named Chaker D. The recipient later told the Tunisian police the money was meant for his brother Meher D. who had left to fight for IS in Libya. Police eventually concluded Meher D. and moumou1 were the same person, according to Thursday reports.

German media  reported that intelligence agencies from both Germany and the US were backing the search for Meher D. He is also reportedly wanted by the Tunisian security forces.

Ever since the Christmas market attack, German security forces have been looking into the remote jihadist mentors whose role is to radicalize, motivate and advise the perpetrators committing the strikes in the West.

The police recently uncovered a suspected terror plot in Cologne, which saw another Tunisian make poisonous ricin for use as a weapon. Investigators are now also investigating the possibility of a remote "instructor" providing guidance to the suspect.

dj/aw (AFP, Reuters, dpa)

Editor's note: Deutsche Welle follows the German press code, which stresses the importance of protecting the privacy of suspected criminals or victims and obliges us to refrain from revealing full names in such cases.