A Pakistani asylum seeker, the only person being held in connection with the attack has been released. German police say the perpetrator may still be at large.
Also in the programme: a river of liquid iron is discovered in the earth's outer core, and the man who photographed the assassination of the Russian ambassador to Turkey.
(Photo: Members of the Germans parliament attend a service at the Church of Remembrance at Breitscheidplatz, the area where a truck ploughed through a Christmas market in Berlin. Credit: Michele Tantussi/Getty Images)