A lorry smashed into a crowded Christmas market in central Berlin on 19 December, killing 12 people and injuring 49, leaving 18 in a critical condition.
The prime suspect, Tunisian man Anis Amri, was shot dead by Italian police on 23 December in the city of Milan after a Europe-wide manhunt.
So-called Islamic State (IS) has said one of its "soldiers" carried out the attack on Breitscheidplatz Christmas market, without offering evidence.
German police had initially detained a 23-year-old Pakistani man, who denied any involvement and was released after questioning.
After an inspection of the lorry, which was registered in Poland, authorities discovered legal identity papers belonging to Amri. Amri's fingerprints were also later discovered in the vehicle's cabin.
It was thought that Amri, 24, had been injured in a struggle with the Polish driver, found murdered in the cab.
Amri was shot dead after firing at Italian police officers who had stopped his car for a routine check, the Italian authorities say.
reportedly pulled a gun from his backpack, shouted "God is greatest" in
Arabic and opened fire, injuring an officer. A second policeman then
returned fire, killing him.
How did the market attack happen?
At 20:14 local time (19:14 GMT) the lorry, laden with steel beams, crashed into people gathered around wooden huts and stands selling mulled wine and sausages.
The market was packed with tourists and locals, at Breitscheidplatz, near Berlin's famous Kaiser Wilhelm Memorial Church.
The lorry drove 50-80 metres (160-260 ft) through the market.
Witnesses reckoned its speed to be about 64km/h (40mph), as it sent market stalls flying, leaving a trail of debris and casualties.