The Nigerians, Ola and Abel Osundairo were said to have been paid by Smollet to stage a physical and homophobic attack against him in January.
The duo have reportedly left the U.S following the staged attack but were apprehended last week when they returned.
They were released without charges after providing information that “shifted the trajectory of the investigation”, police said.
One of the brothers is Smollett’s personal trainer and both have worked as extras on Empire.
Smollett was arrested in Chicago after being charged with filing a false police report.
The actor, who is gay had claimed in his report to the police that he had gone out to buy food late at night in downtown Chicago when “two white men hurled racial and homophobic insults at him”.