Just after 8pm local time, when the Christmas market would have been packed with tourists and locals, a lorry ploughed into the crowd.
Eyewitnesses described hearing a massive bang as the truck veered into the stalls at speed, and then silence.
The lorry which had been loaded with steel beams is believed to have jumped the curb, and drove up to 80 metres into the the market at Breitscheidplatz before coming to a halt on the pavement at the foot of the Kaiser Wilhelm memorial church.
According to police, the suspect fled to a nearby park. A witness followed him for two kilometres before calling the police.
They then arrested a man at the Victory Column monument.
Later the authorities said they couldn’t be sure whether he was the perpetrator.
The body found in the passenger’s seat of the drivers cab was identified as a Polish national, his company confirmed they had lost contact with him around 15:00 GMT on Monday. German magazine Focus Online reported that he had been shot.