Investigations have shown that the man detained Wednesday "is not the suspected contact of Anis Amri," said a spokeswoman for the prosecution.
"He has therefore been released from detention," the spokeswoman, Frauke Köhler, told a press conference.
She confirmed that shortly before Tunisian Amri steered a lorry through a Berlin Christmas market in an attack that killed 12 people, he had sent a mobile phone voice message and a picture to a contact - but said this was not the man who had been detained.
"The investigation into further accomplices or possible people who knew... will continue at full speed," Köhler said.
She also said that a video message released four days after the December 19th rampage, in which Amri is seen swearing allegiance to the head of the Islamic State group, Abu Bakr al-Baghdadi, had been judged authentic.
And the pistol Amri used to fire at an Italian police officer before he was shot dead in Milan last Friday had the same .22 calibre as a bullet that was fired inside the cabin of the lorry.
Investigators were still checking whether it was fired from the same handgun.
The spokeswoman added that the exact cause or time of death of the truck's registered Polish driver, Lukasz Urban, still could not be determined, but that it was "shortly before" the market attack.
The autopsy report was expected in early January, she said, while denying media reports that his corpse bore stab wounds.
Köhler confirmed media reports that the 40-tonne truck came to a rest after 70-80 metres (230-260 feet) thanks to its automatic braking system that activates when impacts are detected.
Federal investigators (BKA) had searched two properties belonging to the 40-year-old Tunisian man, an apartment and a business, in the Tempelhof district in the south of the capital on Wednesday.
Federal investigators announced over Christmas that they were focusing on whether Amri had a support network which helped him carry out the attack and then helped him escape Germany.
"It is very important for us to determine whether there was a network of accomplices... in the preparation or the execution of the attack, or the flight of the suspect," federal prosecutor Peter Frank told reporters.
On December 19th Amri stole a haulage truck and murdered its driver before driving it into a crowded Christmas market in western Berlin.
Twelve people including the Polish truck driver were killed, and dozens were injured, in the attack which has since been claimed by terror group Isis.