Junior was found dead in a Kansas prison on Thursday while he was awaiting trial.
He was 43 years old.
The Kansas City Star reported that a Bureau of Prisons spokesman said that the man was found unresponsive at a federal prison.
He was pronounced dead after being taken to a nearby medical facility.
The Star reported that no other staffers or inmates were injured in the death.
After being hit with a number of criminal charges in the new year, Saousoalii Siavii was being held at the prison.
The former football player was part of a conspiracy to distribute meth. They claim that he had firearms on his person during a wild arrest in August.
After being picked in the second round of the 2004 NFL Draft, he went on to play in 16 games for the Dallas Cowboys.
He played one season for the Seattle Seahawks before his career ended in 2011.
The story is developing.