"This is by no means an accident, this is a mass murder, a cold-blooded killer," the source was quoted as saying.
There is no official confirmation of this information yet. The police said earlier that they were considering all possible options.
The incident happened on Wednesday morning a few hundred meters from Breitscheidplatz, where in 2016 an Islamist drove a truck into a group of visitors to the Christmas market.
As a result, one person was killed while nine others were injured. The driver is a 29-year-old German citizen of Armenian origin, the press service of the city police said, adding that he was detained and is currently preparing for interrogation.