(CNN) -- Aaron Hernandez, the former NFL tight end charged with murder in the death last week of an acquaintance, is now being investigated in connection with a double homicide in Boston's South End in July 2012, a law enforcement source close to the investigation told CNN.
The source gave no indication whether there was any connection between that investigation and Hernandez's current murder charge.
What is known is that the Boston Police Department has located and impounded a silver SUV with Rhode Island registration that police have been trying to find for almost a year, which is linked to the scene of the double homicide, the source said.
Investigators believe that Hernandez was renting the SUV at the time of those killings, the source said.
The development came a day after authorities charged the former New England Patriots player with first-degree murder, accusing him of orchestrating the shooting death of Odin Lloyd last week.
Lloyd's body was found in an industrial park area less than a mile from Hernandez's home. He has pleaded not guilty.
Second arrest in homicide investigation
A second man has been arrested as part of the investigation into Lloyd's death, but authorities haven't provided details.
Carlos Ortiz, 27, was arrested Wednesday in Hernandez's hometown of Bristol, Connecticut. The arrest occurred in connection with the homicide investigation, a Connecticut state prosecutor said in a statement Thursday.
Ortiz was charged as a fugitive from justice, New Britain State's Attorney Brian Preleski said, indicating that documents had been sealed by court order.
In Massachusetts, a warrant for Ortiz's arrest says he faces a charge of possessing a firearm without a license, according to court documents obtained by CNN.
Ortiz spoke with investigators in Connecticut on Tuesday, according to an affidavit filed by a Massachusetts State Police trooper. In that interview, the affidavit says, Ortiz told police that he had been carrying a firearm in North Attleborough, Massachusetts, on June 17 -- the day investigators have said Lloyd was killed.
Details about Ortiz' alleged connection to the Lloyd case were not spelled out in the court documents CNN obtained.
He was being held on $150,000 bond in Hartford on Thursday. He could have an initial hearing in Attleboro, Massachusetts, District Court as early as Thursday, a source with knowledge of the investigation told CNN.
It was not clear from court documents whether Ortiz has an attorney.
New details as bail denied
Hernandez was back in court Thursday to appeal an earlier decision to deny him bail.
A judge at the Fall River, Massachusetts, Superior Court denied his request, saying that bail in first-degree murder cases is very rare, and that Hernandez is a flight risk.
First Assistant District Attorney Bill McCauley, in his argument for why bail should not be granted, provided new details about the investigation.
McCauley revealed that while Hernandez was appearing in court on Wednesday, authorities executed a search warrant on a condo he leases. Inside the condo, they found ammunition for a .45-caliber weapon -- the same caliber of weapon investigators believe was used in Lloyd's slaying, the prosecutor said.
And inside a silver Hummer registered to Hernandez in front of the condominium, investigators found a clip to a .45-caliber firearm, McCauley told the judge Thursday.
Lloyd was shot five times, he said.
The first bullet went through his forearm and into his abdomen, suggesting that he tried to raise his arm to defend himself, McCauley said. Lloyd was then shot twice in the back and, once he was down, two more times in the chest, the prosecutor said.
The murder weapon hasn't been found, McCauley said.
Chilling text messages
Lloyd sent a series of messages his sister early last Monday morning, McCauley said.
"Did you see who I am with?" he wrote in one message, according McCauley.
When she asked who, he replied, "NFL."
Then Lloyd wrote, "Just so you know," McCauley said.
That was a sign, the district attorney argued, that Lloyd knew he was in peril.
Defense attorney: Hernandez is 'one of the best football players'
Hernandez's lawyers, arguing for bail, said their client had not obstructed the investigation, as prosecutors alleged, and was not a flight risk.
Defense attorney James Sultan stressed what he called Hernandez's professionalism.
"Mr. Hernandez is not just a football player," he said, "but is one of the best football players in the United States of America."
He also noted that Hernandez was recovering from shoulder surgery and attends physical therapy and sees doctors on a regular basis.
And he argued that Hernandez had told investigators that he would turn himself in if they had a warrant for his arrest.
"They chose not to do that. They wanted to arrest him in his house, to drag him, to arrest him in front of his fiancée and his baby and to drag him out in handcuffs in front of the media," Sultan said. "That was their choice."
Defense attorneys offered the use of electronic monitoring and house arrest as options, but those were rejected.
Accusation of orchestrating murder
On Wednesday, McCauley said in court that Hernandez "drove the victim to the remote spot, and then he orchestrated his execution."
"He orchestrated the crime from the beginning, he took steps to conceal and destroy evidence, and he took steps to prevent the police from speaking to ... an important witness," the prosecutor said.
Defense attorney Michael Fee has said that the evidence is circumstantial and that bail should be granted so that Hernandez can return home to spend time with his fiancee and 8-month-old child.
"It is a circumstantial case. It is not a strong case," Fee said, arguing that Hernandez was not a flight risk and had cooperated with authorities.
Lloyd, 27, was a semipro football player who worked for a landscape company. His sister, Olivia Thibou, told CNN last week that her brother was dating the sister of Hernandez's fiancee. Lloyd and Hernandez were at a Boston nightclub together the night of June 14, she said.
A 'model inmate'
During his first 24 hours in jail, Hernandez has been "polite and cooperative" and a "model inmate," Bristol County Sheriff Tom Hodgson said.
Hernandez was being held in the jail's medical unit, which is standard for someone who hasn't been incarcerated before, Hodgson said.
The former pro athlete showed "no apparent nervousness" in jail, Hodgson said, but he noted the difficulty of going from having thousands of people cheering for him to being "just a number."
While in the medical unit, Hernandez will be locked up for 23 hours a day, with a break for a shower and phone calls, the sheriff said.