Hernandez, a former National Football League star who played with the New England Patriots, was already convicted of first-degree murder previous year in the 2013 shooting death of Odin Lloyd and is now serving a life sentence.
Opening statements for the case are not scheduled until March.
Hernandez, 27, was a star tight end for the New England Patriots. Prosecutors say Hernandez shot Bradley in the face in 2013 because he was anxious Bradley might implicate him in the double slaying.
Former New England Patriots NFL football player Aaron Hernandez, left, sits beside his attorney Jose Baez during a status conference in his upcoming double murder trial, Wednesday, Oct. 5, 2016, at Suffolk Superior Court in Boston.
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He was indicted for the murders in 2014, and pleaded "not guilty" to both counts.
According to the source, prosecutors said Hernandez orchestrated and tried to cover up the death of Lloyd, whose body was found in an industrial park just a mile from Hernandez's home.
As Hernandez was introduced to the juror pool, several people re-positioned themselves just to get a glimpse of him. Clearly, Hernandez didn't want to show his face and the judge even asked about his hand tattoo, as the tattoo was also a subject that is expected to come up during the trial of the heavily inked Hernandez.
A judge ruled last month that prosecutors would be able to access the text messages Hernandez sent to his sports agent and discuss his tattoos, which the state has argued are an admission of his guilt, The Boston Globe reports. Prosecutors claim that Hernandez fired five shots into the two men's auto as they sat at a red light.