The men arrested have been identified as 25-year-old Abel Osundairo and brother Ola Osundairo, 27, who hail from Nigeria.
"Detectives have probable cause that they may have been involved in an alleged crime and we are working to corroborate the allegations and investigative timeline as our investigation continues," Chicago police spokesman Anthony Guglielimi said in a statement Friday.
Police say the two brothers are the shadowy figures caught on surveillance cameras shortly before the alleged attack. They have denied any wrongdoing.
Smollett says he's certain the two men in the photograph are the men who attacked him.
“I don't have any doubt in my mind that's them. Never did,” he told ABC News.
Both men have links the 36-year-old actor and have appeared as extras on “Empire.” Ola appeared in a scene with Taraji P. Henson and Terrence Howard.
The brothers flew to Nigeria hours after the alleged attack. Video on social media shows one of them giving money to an injured teenager there.
They returned to Chicago's O'Hare Airport on Wednesday at 5:45 pm, where detectives were waiting for them.
Police searched their apartment in Chicago hours later. A handwritten inventory shows they took away bleach, black face mask, a red hat, an “Empire” script, a laptop and receipts.
Questions have been raised about whether the reported attack actually happened.
Thursday morning Smollett talked about the attack on “Good Morning America” with Robin Roberts. At 7:42 a.m., while the show was still on the air, police revealed they were questioning two "persons of interest."
A blizzard of apparently conflicting information followed.
At 7 p.m., police said they were "investigating ... whether an attack happened at all."
On Friday at 8 a.m., police said, "There is no evidence to say this is a hoax."
“While we haven’t found any video documenting the alleged attack, there is no evidence to say that this is a hoax,” Guglielmi told the Los Angeles Times in a statement. “The alleged victim is being cooperative at this time and continues to be treated as a victim, not a suspect.”
Meanwhile, 20th Century Fox slammed media reports that Smollett was being written out of the hit show.
“The idea is patently ridiculous he remains a core player on this very successful series and we continue to stand by him,” they said in a statement.