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 Polish driver who was the first victim of the lorry attack at Berlin's Christmas market was found stabbed and shot to death on the passenger seat, his cousin has said.
Ariel Zurawski, who owns the lorry company, said the German authorities asked him to identify 37-year-old cousin Lukasz Urban from photographs taken at the scene.
Mr Zurawski told reporters Mr Urban had arrived in Berlin on Monday morning whereupon he was told to delay his delivery until Tuesday morning.
He said Mr Urban spoke briefly to his wife by phone around 3pm local time on the day of the attack while she was working.
He said Mrs Urban called her husband back at 4pm but he did not answer his phone.
The attack outside the Kaiser Wilhelm Memorial Church took place at 8pm.
Polish Prime Minister Beata Szydlo earlier confirmed "with pain and sadness we received the information that the first victim of this heinous act of violence was a Polish citizen".
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?