Jurors in the double murder trial of former New England Patriots star Aaron Hernandez heard chilling testimony on Tuesday from an eyewitness to the 2012 shootings.

Around 2:30 a.m. on July 16, 2012, Brian Quon and Donald Gobin had finished their shift working security at Underbar in Boston when they encountered the shooter’s SUV at a stoplight at Shawmut Avenue and Marginal Road, Quon testified Tuesday in Suffolk Superior Court.

The SUV pulled up “extremely close’’ to the passenger side of the sedan Gobin was driving, Quon said. The driver of the SUV looked into the Saturn, said Quon, who was seated in the sedan’s front passenger seat.

Quon said the SUV abruptly sped through the red light and caught up with a BMW at Shawmut Avenue and Herald Street. At that point, Quon testified, he heard “bam bam bam bam bam bam,’’ and told Gobin “that sounds like gunshots.’’

His suspicions were confirmed when the Saturn slowly pulled up to the BMW. Quon noticed shattered glass around the car and said the front passenger “appeared to be dead . . . it was all bloody on his shirt.’’

The driver was “just taking his last breath,’’ Quon said.

The SUV fled the scene by turning left, Quon testified.

Prosecutors allege that Hernandez fired the shots from the passenger seat of the SUV, which was driven by his friend and marijuana supplier Alexander Bradley.

Hernandez has pleaded not guilty to charges of fatally shooting Daniel de Abreu and Safiro Furtado as they sat in the BMW.

On cross examination Tuesday, defense attorney Ronald Sullivan zeroed in on statements Quon previously made that the SUV passenger appeared to be a thin, black woman with braids or cornrows.

Sullivan played an audio recording of Gobin’s 911 call, and Quon can be heard in the background saying the SUV passenger “looks like a female.’’

The lawyer also referenced Quon’s grand jury testimony when he said the passenger was black, either male or female.

Quon told police three days after the shootings that the passenger appeared to be a skinny black female with cornrows, Sullivan said.

“I believe I told them it was either a male or female,’’ Quon said.

Suffolk County prosecutor Patrick Haggan highlighted other portions of Quon’s police interview and grand jury testimony, including when he told investigators he “couldn’t really see the face’’ of the passenger or determine the person’s gender.

Earlier in the day, relatives of de Abreu and Furtado cried as jurors viewed graphic photos of the slain men.

The photos were not displayed on courtroom monitors, but two women seated in the family section dabbed their eyes with tissues as jurors passed around pictures of the bloodied bodies.

Superior Court Judge Jeffrey Locke told jurors they could not allow their emotions to color their judgment.

“They can be disturbing to view,’’ Locke said of the images, adding that jurors “must remain dispassionate throughout.’’

Hernandez is serving a life sentence for the June 2013 fatal shooting of Odin Lloyd, a 27-year-old Dorchester man who dated the sister of Hernandez’s fiancée.

Testimony in the trial resumes Wednesday.

Travis Andersen can be reached at tandersen@globe.com.