BBC....
Germany's Interior Minister Thomas de Maiziere has given a few more details about the arrested suspect.
He is from Pakistan, arrived in Germany on 31 December last year and came to Berlin in February. He then attempted to bring relatives over to Germany.
His asylum claim has not yet been decided upon. His name appeared in some official databases, but not in anti-terror ones.
Mr de Maiziere also said the pistol apparently used to kill the man found dead in the passenger seat of the truck passenger has not yet been found.
Germany's
Die Welt newspaper is quoting a "high-raking security source" as saying the arrested Pakistani man is not believed to be the person who carried out the deadly attack.
The man has denied any involvement.
"The real attacker is still armed and on the loose and can do more damage," the source told the newspaper.
Police and special units have been informed, the source told Die Welt.