Hundreds of people are pausing at a make shift memorial in Berlin near the site of Monday's attack that killed 12 and injured at least 50.
The perpetrator of the bloody attack on a Berlin Christmas market could still be at large after police admitted they have no weapon and are "uncertain" the right suspect is in custody.
A 23-year-old Pakistani asylum seeker known only as "Navad B" is in custody after the deadly attack that killed 12 and injured up to 50 people on Monday evening when a truck ploughed into festive shoppers.
However police said they are not yet sure whether he was responsible for the attack or is part of a wider group. At a press conference on Tuesday Berlin's Police Chief Klaus Kandt said: "It is indeed uncertain he was the driver" of the truck that smashed through market stalls.
Security has been stepped up at Christmas markets across the capital. Photo / AP
Police are waiting on the results of DNA tests from inside the cab of the truck and gunpowder residue from the scene. They are asking people to remain vigilant amid a high-level security threat.
German Interior Minister Thomas de Maiziere said the man in custody "comes from Pakistan". He has denied being involved in the event and it's thought he arrived in the country between December 31 2015 and February 2016 via the Balkans route.
He was reportedly arrested 2.5 kilometres away from the market. Eyewitnesses report seeing a man flee the cab of the truck, pulling off a mask as he ran.
German chancellor Angela Merkel arrives at the scene of the tragedy. Photo / AP
Truck computer provides clues
The chaos comes as police scour the on-board computer of the truck for clues as to what happened in the hours before it ploughed into crowds.
Berlin police have confirmed the man found dead in the truck was not in control of it when it drove into the festive Breitscheidplatz markets. He has been named by as 37-year-old father of one Lukasz Urban .
It's believed the truck was hijacked at a depot before being driven into the market around four hours later.
The on-board computer shows at 3:44pm on Monday someone tried to start it before another attempt at 4:52pm. By 5:37pm the truck's engine was turned over again suggesting that someone unfamiliar may have been attempting to drive it.
By 7:34pm it began to move before driving into crowds at 8:15pm.
A woman is illuminated by candles as she cries in Berlin. Photo / AP
"First hot lead"
An elite unit of armed police stormed disused Tempelhof Airport at 4am on Tuesday morning.
The site, which was built by the Nazis in the 1930s was closed years ago and has been converted to temporary accommodation for nearly 2000 refugees. Germany has accepted an estimated one million refugees since the 2015 crisis after Chancellor Angela Merkel welcomed Syrian refugees into the country.
On Tuesday, Ms Merkel said she was "shocked" at the attack which appeared to be Islamist terror, as far-right leaders warned "the horror has arrived" in Germany.
Berlin police said the truck attack at Breitscheidplatz was deliberate and said they are working at "full steam" to find those behind it. German television station N24 said the airport site provides the "first hot lead" after the attack. It's believed no arrests were made.
The trailer of a truck stands beside destroyed Christmas market huts. Photo / AP
Police said on Twitter "The man who was found dead in the truck did not control the truck".
"Our investigators assume that the truck was deliberately steered into the crowd at the Christmas market at Breitscheidplatz."
"All police measures related to the suspected terrorist attack at Breitscheidplatz are progressing at full steam and with the necessary diligence."
Onlookers were terrified on Monday evening when the large truck drove straight through stalls at the festive markets that were filled with locals and tourists drinking mulled wine and watching the Christmas lights.
The truck used in the carnage had Polish licence plates and the owner of the company claimed it was hijacked.
The truck which ran into a crowded Christmas market killing several people. Photo / AP
"We haven't heard from him since this afternoon. We don't know what happened to him," Ariel Zurawski said about the driver.
"He's my cousin, I've known him since I was a kid. I can vouch for him."
Australian woman Trisha O'Neill said she was at the market with friends when she saw "blood and bodies everywhere".
"I just saw this huge black truck speeding through the markets crushing so many people and then all the lights went out and everything was destroyed," she told the ABC.
"I could hear screaming and then we all froze." Ms O'Neill, who moved to Germany in September, burst into tears when she saw how many people, including children, were laying on the ground.
"I never thought I would see something like this in my life," she said.
