In it he claimed he was assaulted by two masked men who hurled racist and homophobic slurs.
The second has to do with what Smollett told police in an interview.
Mr Smollett is accused of paying two brothers to stage the attack. The letter is now in the FBI crime lab for analysis, sources said, and experts believe Smollett could face federal charges for allegedly sending the letter.
His attorneys said after his arrest on February 21 they were conducting a thorough investigation for purposes of mounting the actor's defense.
What did he say happened?Smollett also told police that the assailants "yelled pro-'Make America Great Again' [MAGA] comments" during the attack.
How has the case unfolded?
Prosecutors also alleged that Smollett told the brothers what to say and provided them with a $100 bill to cover supplies, including rope, ski masks and red hats that resemble the MAGA sort.
He told Baig that he had been attacked by two "unknown males" who were dressed in black. "You said they changed their story in the 48th hour - why did they change their story?" The men were released without being charged.
But skepticism about Smollett's account grew as police continued to investigate, questioning two "persons of interest" who turned out to be brothers of Nigerian descent who had previously worked on Fox's "Empire".
While being questioned by investigators, the brothers claimed that Smollett paid them $3,500 to help orchestrate and stage the crime after he became upset that a threatening letter addressed to him and delivered on January 22 to the Fox studio where "Empire" is filmed did not get enough attention, law enforcement sources told ABC News.
Chicago Police Superintendent Eddie Johnson said the actor initially faked a letter using racist and homophobic language. "How could someone look at the hatred and suffering associated with that symbol and see an opportunity to manipulate that symbol to further his own public profile?" He posted bond and was released from custody shortly before 4 p.m. Smollett did not speak as he left the Cook County Jail, and was blocked from the crush of media and cameras by a large bodyguard, whose shoulders he held onto.