Three people including the nephew of the Berlin Christmas market attacker Anis Amri have been arrested in Tunisia.
Tunisia's Interior Ministry said Amri - who was shot dead on Friday - had sent his 18-year-old nephew Fedi money to join him in Europe.
Twelve people were killed and dozens more injured in the attack on Monday.
The mother of Berlin attack suspect Anis Amri has said she fears the world will now never know why he allegedly drove a lorry through a crowd.
Nour El Houda Hassani said "they killed my son with all his secrets."
Speaking in his Tunisian hometown of Oueslatia, she begged for his remains to be brought home "I want to know the truth of my son, I want to know who was behind him, I want to know who brainwashed him."
Amri was shot by Milan police on Friday after his identity papers and fingerprints were found on the truck used in Monday's attack, which killed 12 and injured dozens.
The Islamic State group released a video in which Amri pledged allegiance to the extremists.
The funeral for the lorry driver killed in the Berlin Christmas market attack has taken place in his home country of Poland.
Footage has emerged of the final moment before a truck ploughed into a crowd of people at a Christmas market in Berlin.
A man is being hunted by German police after a lorry ploughed into a Berlin Christmas market on Monday, killing 12, but who is the suspect?