Hernandez's lawyer countered that the NFL player had "the world at his feet" and had no reason to kill. He repeatedly told jurors that the athlete is innocent and said authorities "locked" in on him as a suspect early on, ignored evidence and conducted a "sloppy and unprofessional" investigation.
Hernandez, 25, is charged in the 2013 shooting death of Odin Lloyd, a 27-year-old semipro football player who was dating the sister of Hernandez's fiancee. Lloyd's bullet-riddled body was found in an industrial park near Hernandez's North Attleborough home, not far from Gillette Stadium.
Hernandez — who had a $40 million contract as a tight end but was cut by the Patriots just hours after his 2013 arrest — could get life in prison if convicted. On Sunday, the Patriots will meet the Seattle Seahawks in the Super Bowl.
In a separate murder case that has yet to come to trial, Hernandez was charged last year in Boston with killing two men in 2012 after someone spilled a drink on him at a nightclub.
Prosecutors in this trial have suggested that Lloyd may have been killed because he knew too much about that crime. But the judge has ruled that prosecutors cannot tell the jury about those slayings.
In opening statements Thursday, District Attorney Patrick Bomberg showed the jury before-and-after security video to connect Hernandez to Lloyd's killing.
He played footage that he said showed Lloyd getting into a Nissan Altima rental car driven by Hernandez, then video from the NFL player's home, taken shortly after Lloyd was killed, without Lloyd in the car.
Prosecutors say Hernandez and two of his friends drove Lloyd to the industrial park and shot him. The two friends are awaiting trial.
The prosecutor also presented an image taken off Hernandez's video surveillance system that showed Hernandez standing outside his basement, holding what Bomberg said was a gun.
He said a marijuana joint found near Lloyd's body had Hernandez's and Lloyd's DNA. Hernandez's DNA was also on a shell casing from a bullet found under the driver's seat of the rental car, Bomberg said. He told jurors that the casing was fired by the same weapon as casings found at the crime scene: a .45-calibre Glock.
As the prosecutor showed jurors a photo of Lloyd's body, his mother was overcome and had to leave the courtroom briefly.
Defence attorney Michael Fee told the jury that Hernandez is an innocent man.
"Aaron never had a chance," Fee said. "They locked on Aaron and they targeted him."
He said the evidence would show that Hernandez did not kill Lloyd and did not ask anyone to do so. He said authorities could offer no motive for the killing.
"The investigation was sloppy and unprofessional. What about the facts that showed Aaron's innocence?" he said. "The evidence will show that they were ignored."
Noting that Hernandez had long-term football contract, a new house, a fiancée and a 7-month-old baby, the defence attorney said Hernandez "was planning a future, not a murder."
Evidence that Hernandez was at the scene is not enough to convict him, Fee said.
"Mere presence is not enough," he told the jury. "We can't be convicted of a crime just because we hang with the wrong people or are in the wrong place."
Hernandez often leaned forward in court, paying close attention to opening statements and witness testimony, including the account of Matthew Kent, who was a high school freshman when he found Lloyd's body while jogging.
Hernandez's fiancée, Shayanna Jenkins, sat behind him with Hernandez's brother, DJ, who coaches college football in Iowa.