(CNN) -- Former New England Patriots star Aaron Hernandez -- already charged in the 2013 slaying of a semipro football player -- is expected to be indicted Thursday in connection with a 2012 Boston double homicide, a law enforcement source with knowledge of the case said.
A grand jury had been looking into whether Hernandez played a role in a drive-by shooting that killed Daniel Abreu and Safiro Furtado in July 2012, according to law enforcement sources. Authorities said Abreu and Furtado were in a BMW outside a Boston nightclub when they were shot.
That shooting is separate from a 2013 killing in which Hernandez, 24, was arrested and charged last summer.
It first became public that Hernandez was suspected in the Boston murders when documents were unsealed in court in January.
In those records, it is suggested that Hernandez was the trigger man in Abreu and Furtado's killings.
"There is ... probable cause to believe that Aaron Hernandez was operating the suspect vehicle used in the shooting homicides ... and may have been the shooter," reads a June 2013 warrant that was part of the unsealed batch of records.
The warrant was used to search a Toyota 4Runner linked to Hernandez that, according to court documents, witnesses saw at the scene of the crime. The warrant gave permission to search for gun residue on the SUV, which was recovered at the home of Hernandez's uncle in Bristol, Connecticut.
In search warrant affidavits, investigators have said Hernandez and another man, later identified as Alexander Bradley, followed Abreu and Furtado into the club.
The former star football player and Bradley are seen on security cameras together inside Cure Lounge and also driving an SUV that had been following Abreu and Furtado when they left the club, according to court papers. Witnesses said that the SUV sped away after multiple shots were fired at the BMW.
In February, the Abreu and Furtado families filed wrongful death lawsuits against Hernandez, with each family seeking $6 million.
June 2013 shooting
There has been a focus on Hernandez since he was arrested in June. He was charged with first-degree murder and weapons charges in connection with the June 17 shooting death of 27-year-old semipro football player Odin Lloyd in North Attleboro, Massachusetts.
On June 17, a jogger found Lloyd's body riddled with gunshot wounds at an industrial park in North Attleboro.
Prosecutors have said that on that day, Lloyd was seen was seen around 2:30 a.m. with Hernandez and Hernandez's friends, Carlos Ortiz and Ernest Wallace, in a rented silver Nissan Altima.
On June 18, police searched Hernandez's home about a mile from where the body was found, and they searched it again on June 22. Days later, the football player was arrested and charged with first-degree murder for Lloyd's death. Hernandez also was hit with five weapons-related charges.
In court on June 26, First Assistant District Attorney Bill McCauley said that Hernandez "drove the victim to the remote spot, and then he orchestrated his execution."
"He orchestrated the crime from the beginning," McCauley said. "He took steps to conceal and destroy evidence, and he took steps to prevent the police from speaking to ... an important witness."
Hernandez pleaded not guilty, and a judge ordered him held without bail.
The NFL's Patriots then dropped the tight end from the team roster.
At the June 26 hearing, defense attorney Michael Fee said that the evidence against his client was circumstantial and that bail should be granted so that Hernandez could return home to spend time with his fiancee and his then-8-month-old child.
"It is a circumstantial case. It is not a strong case," Fee said, arguing that Hernandez had cooperated with law enforcement and was not a flight risk.
While investigators worked, and the former football star stayed behind bars, the Lloyd case took several twists and turns.
Last September, Hernandez's associate, Wallace, pleaded not guilty to being an accessory after the fact of a slaying in Lloyd's death. That month Ortiz, 27, of Bristol, Connecticut, was also indicted on a single count of accessory to murder after the fact, in connection with the killing of Lloyd. He pleaded not guilty.
Among Hernandez's jail visitors have been his fiancee, Shayanna Jenkins, and cousin, Tanya Cummings Singleton, both of whom face charges in connection with the Lloyd homicide, the court papers revealed in February.
Last October, Jenkins pleaded not guilty to perjury charges after prosecutors alleged that she lied to a grand jury and disposed of evidence.