Swedish authorities have strenuously denied this allegation, with the country's prime minister, Stefan Löfven, saying politicians should not interfere with judicial matters.
On Tuesday, after almost a month in prison, Mayers, 30, and the two other suspects pleaded not guilty to assault. They say that they were acting in self-defense after being harassed by two men, one of whom is the alleged victim, Jafari.
Prosecutor Daniel Suneson showed the judge video from security cameras and witnesses' phones, which he said supported the case against the defendants. The prosecution alleges that Mayers threw Jafari on the ground, before he and two of his entourage kicked and punched him.
Jafari claims he was hit over the back with a bottle. The defense says there is no evidence for this.
"I was shocked that he took me by the neck and lifted me up," Jafari told the court. "I tried to hit him but my [punches] did not land."
He said he and his friend followed the rapper and his associates because he threw his headphones at the group and wanted them back.
"I went after them because I could not speak English and I wanted to know why he behaved that way," he said. "I wanted my headphones back."
Throughout most of the evidence and testimony, Mayers looked straight ahead expressionless.
The case has gathered so much media attention that Tuesday's hearing had to be held in a special secure courtroom. Among those present were some 50 journalists and a U.S. diplomat, Robert C. O'Brien, who is the State Department's special presidential envoy for hostage affairs.
The three defendants entered the room wearing handcuffs and prison uniforms of green T-shirts and pants.
The alleged victim is seeking 139,000 Swedish crowns (around $14,500) in damages. If convicted the defendants could face two years in jail.
Mayers' team is expected to present its evidence on Thursday and a verdict could be reached as early as Friday.
Alexander Smith reported from London, and Alex Ponomarev reported from Stockholm.