According to CCTV footage, Magnitz was attacked from behind by one of three men that were seen on video, Frank Passade, spokesman for the Bremen public prosecutor's office said.
As a result of this, Magnitz fell. The investigators said it's likely he sustained his injuries in the fall.
This contradicts what the AfD said about the attack, or that Magnitz had been beaten by a piece of wood until he was knocked unconscious and then kicked while he was on the ground.
“We assume that all the injuries are solely due to the fall,” Passade told DPA on Wednesday.
The AfD group had published a photo of Magnitz unconscious on a hospital bed, his face bleeding and swollen with a gash on his forehead. They then said three masked men had carried out the attack.
“They hit him with a piece of wood until he was unconscious and then kicked him on the ground,” a statement from the party said on Tuesday, adding that a construction worker had intervened to stop the assault.
The party had issued the statement following a visit to Magnitz, 66, in hospital on Monday evening after the incident.
The perpetrators ran away immediately after the attack, Passade said, according to the footage.
Police on Tuesday said they believed it had been a “politically motivated” attack.
It also drew international attention, as it appeared to highlight Germany's increasingly fraught political landscape.
Magnitz, who is still in hospital, had told DPA that he neither saw the attackers nor heard them say anything.
“I will in any case be more careful when walking through the area,” he said, adding that doctors were likely to keep him in hospital until the weekend.