Mr Brown, 35, and his mother Myrtle Brown, 73, had been reported missing by a worried family member on Saturday.
One day later, Myrtle’s body was found in the Addison Creek Reservoir, less than 100 yards from her home in the small suburban village of Maywood.
The Cook County Medical Examiner’s Office confirmed her cause of death to be a homicide.
Mr Brown was deemed missing following his mother’s murder, with no sign of the former New England Patriots star.
Now, in a shocking turn of events, Mr Brown has now turned up on Instagram – posting a bizarre video claiming that he believed his mother was holiday and that he had been kidnapped by law enforcement.
The video was first reported by Fox32 and appears in an Instagram story on account “intplayerwithapassport”, and not the former player’s verified account.
The Independent has not been able to independently verify that the account belongs to Mr Brown.
In the video, Mr Brown starts off by hitting out at “fake news” before launching into incoherent ramblings about the FBI.
He claims that he thought his mother was on vacation and makes accusations against Maywood Police and the FBI, saying that he was “kidnapped” twice by either one of them.
The Independent has contacted the FBI and Maywood Police Department for comment.
Mr Brown has not been named as a suspect in his mother’s murder.
The 35-year-old had an NFL career that took off in 2010 when he was signed by the New England Patriots. He also played with the Indianapolis Colts, Buffalo Bills and Jacksonville Jaguars, before he was dropped by the Jaguars in 2016.
Since then, he has led a quiet life out of the sporting spotlight.
Before the disappearance of him and his late mother last week, neighbours claim they noticed an odd change in his behaviour.
Carlos Cortez told WBBM that Mr Brown’s family said “he wasn’t himself the last few months”
“He was out of his mind,” he said.
The neighbour said that he had also given authorities Ring doorbell video, in which Mr Brown is reportedly seen burning his mother’s clothes.
“They seen him taking out the trash, and they seen him have a bonfire where he burned all her clothes,” he said.