(CNN) -- Former New England Patriots tight end Aaron Hernandez, jailed on a murder charge, declared his innocence as he responded to a fan letter, saying that "all the people who turned on me will feel like crap," according to a report.
TMZ, which on Thursday published the letter online, said it has independently verified its authenticity with authorities.
Massachusetts authorities have accused the fallen NFL star of orchestrating the June 17 shooting death of Odin Lloyd, the 27-year-old boyfriend of Hernandez's fiancée's sister. Hernandez has pleaded not guilty to murder and is being held without bail.
In the letter, Hernandez responded to the fan, "The world just makes things out of false accusations and it will all die down especially when they say NOT GUILTY......"
At the end of the letter, Hernandez pleads for the letter not to be leaked to social media.
The fan, who does not want to be named, sold the letter to Sportsworld in Saugus, Massachusetts, according to Phil Castinetti, owner of the memorabilia shop. Sportsworld then sold the letter to TMZ for $18,000, according to the shop's Brendan Brennan, who declined to say how much the business paid the fan for the letter.
So much for keeping it off social media.
But the fan said he sold the letter for good reason.
"I wanted to show him that I'm supporting him," the fan told CNN on Friday. "I don't think it's right because people haven't heard his side of the story. All you see is Twitter and Facebook saying bad things. People need to see that he took his time to write somebody a letter back," he said.
Although he is supporting Hernandez, the fan still sympathizes for the family of the victim.
The fan wrote the letter two weeks ago, but said he didn't expect to hear back. The fan mentioned in the letter his own troubles with the law and how he was able to turn his life around.
He added to the letter photos of Hernandez, his fiancée and their daughter, which Hernandez now has on his wall in the cell, as "something to look at beside those four walls," according to the fan.
CNN cannot independently confirm this account.
"I know there is a reason I'm going thru this and I will figure it out through my relationship with the Lord," continued Hernandez in the letter, according to TMZ.
Bristol County Sheriff Tom Hodgson told CNN that the envelope and stationery came from Bristol County House of Corrections, but could not confirm whether Hernandez actually wrote it.
However, the name "Aaron Hernandez," the identification number, unit and room number were listed on the outgoing envelope.
A spokesperson for a law firm representing Hernandez declined to comment.
At the bottom, after his signature, Hernandez said "Can't wait to sign this again when I'm playing again and prove all the haters and [....] talkers WRONG."
CNN's Dominique Debucquoy-Dodley and Chris Welch contributed to this report.