Two men were with Aaron Hernandez on the night he allegedly killed Odin Lloyd, and their testimony could be crucial for prosecutors as they try to build a solid case against the former Patriots tight end.

Yet already, the credibility of the prosecution's key witness, Carlos Ortiz, has come into question after Ortiz changed his story about what happened that night in June.

During a bail hearing Thursday for Hernandez's co-defendant, Ernest Wallace, an assistant DA revealed that Ortiz now claims that Wallace never got out of the car in the industrial park where Lloyd's body was found. Ortiz previously told prosecutors multiple times that Hernandez drove to the industrial park, and then got out with Wallace and Lloyd while he remained behind in the car. Ortiz, according to court documents, told investigators he heard gunshots before Wallace and Hernandez returned to the vehicle.

Wallace has been charged as an accessory to murder, while Ortiz has only been hit with a gun charge.

Of the three defendants, only Ortiz has cooperated with investigators, offering testimony that has later been corroborated by other evidence, including surveillance footage from Hernandez's home.

Also problematic for Ortiz's credibility is a white towel found feet from Lloyd's body. As Fox Sports reported earlier this month, surveillance footage from a gas station caught Ortiz wearing a white towel around his neck, a detail prosecutors could use to question whether Ortiz was lying about not leaving the car.

Such a discrepancy could leave "a hole in your case big enough to drive a truck through," Boston College law professor R. Michael Cassidy told Fox Sports.

"If you're lying about getting out of the car, why should we believe anything else you say?" Casidy added, sampling a potential line of cross examination.

Hernandez's lawyers have claimed all along that the evidence against their client is merely circumstantial. And investigators have yet to find the murder weapon, which would be a crucial piece of hard evidence if it were ever tied back to Hernandez.

Still, Bristol District Attorney Samuel Sutter said he was "not at all" worried that the shifting story could scuttle the prosecution's case.

The prosecution has presented extensive evidence proving Hernandez was at least with Lloyd on the night he was murdered, including text messages between the two. It has also produced surveillance footage showing Hernandez in his home with a gun. And at the same Thursday hearing, prosecutors disclosed that Hernandez had made several phone calls to Wallace immediately after police first came to his home with questions about Lloyd.