Hernandez was in court for what was supposed to be a probable cause hearing, but prosecutors said the grand jury is still considering the evidence against him.
Judge Daniel O'Shea considered defence objections to a delay but decided to reschedule the hearing for Aug. 22. Hernandez will continue to be held without bail until then.
Hernandez has pleaded not guilty to murder in the death of Odin Lloyd, a 27-year-old Boston semi-professional football player whose body was found June 17 in an industrial park near Hernandez's home. He had been shot five times.
Bristol County Assistant District Attorney William McCauley said additional evidence includes boxes of ammunition found at a condominium Hernandez leased and a magazine for a .45-calibre Glock in a Hummer registered to him. Authorities say Lloyd was killed with a .45-calibre gun, though it apparently has not been recovered. McCauley said the ammunition box had Hernandez's fingerprints on it.
Hernandez attorney James Sultan objected to the delay, saying his client has already been jailed for four weeks and that the district attorney could have waited to bring charges, but chose to go ahead last month.
"He made it sound like a slam dunk case," Sultan said.
Outside court, another of Hernandez's attorneys, Charles Rankin, said he was "extremely disappointed" that prosecutors weren't prepared to go forward and that he's confident Hernandez will be exonerated.
Hernandez's girlfriend, Shayanna Jenkins, was in court for the hearing — Hernandez mouthed "I love you" in her direction before he was led out — but she did not respond to reporters' questions as she left the courthouse.
Members of Lloyd's family also attended the hearing but did not comment.
Also Wednesday, O'Shea ruled in favour of media organizations, including The Associated Press, that were seeking access to more documents in the case, including two arrest warrants, additional search warrants and other materials. The records will be released at 3 p.m. Thursday if no one appeals.
Sultan objected to the documents' unsealing, saying he understood the media's "insatiable appetite" but that the release of records is undermining Hernandez's right to a fair trial.
Prosecutors say Hernandez orchestrated Lloyd's killing because he was upset at him for talking to people Hernandez had problems with at a nightclub a few days earlier.
They say Hernandez and two associates, Ernest Wallace and Carlos Ortiz, drove with Lloyd to the North Attleborough industrial park. Authorities have not said who fired the shots, but documents filed in Florida — and released since Hernandez's last court appearance — paint the former Patriot as the triggerman. According to the records, Ortiz told police that Wallace said Hernandez fired the shots.
Hernandez was kicked off the team within hours of his arrest. New England Patriots coach Bill Belichick broke his silence Wednesday, saying the Patriots will learn from "this terrible experience," and that it's time for New England to move forward.
"We'll continue to evaluate the way that we do things, the way that we evaluate our players and we'll do it on a regular basis," Belichick said. "I'm not perfect on that, but I always do what I think is best for the football team."
Wallace and Ortiz also are facing charges. Wallace pleaded not guilty to a charge of being an accessory to murder after the fact. Ortiz has pleaded not guilty to a gun charge.
Warrants released Tuesday in Hernandez's hometown of Bristol, Conn., show police found ammunition, a gun box and documents tied to Ortiz and Wallace at Hernandez's uncle's home.
The warrants were used to search that home, where Ortiz said he lived; an apartment also linked to Ortiz; and a rental car police say was used by Wallace and Ortiz to return to Connecticut after the shooting.
The items seized from the home included clothes, Correction Department documents linked to Ortiz and Wallace, a plastic gun box and two boxes of .38-calibre ammunition.
Bristol police also have been investigating a possible link to a 2012 double fatal shooting in Boston, and earlier said they had seized an SUV wanted in that investigation from the uncle's home. Court records say it had been rented in Hernandez's name.
Associated Press sports writer Howard Ulman in Foxborough and AP writer Pat Eaton-Robb in Hartford contributed to this report.