The trial of Alec Baldwin took a dramatic turn on Friday when a manila envelope of previously unexamined evidence was brought into the courtroom, prompting the judge to put on blue latex gloves, cut it open with a pair of scissors and then get down from the bench to examine ammunition in the well of the courtroom.

It was an unusual scene in a case that has seen dramatic twists and turns for more than two years.

Lawyers for Mr. Baldwin, who is on trial for involuntary manslaughter for his role in the fatal shooting of the cinematographer on the set of the film “Rust,” called for the case to be dismissed on Friday, accusing the prosecution of hiding evidence that could help explain how live ammunition wound up on a film set where it was supposed to be banned.

“They buried it,” Luke Nikas, a lawyer for Mr. Baldwin, said in court, accusing the prosecution of failing to disclose that it was given a batch of rounds said to be connected to the case when the defense asked to review all the ballistic evidence. “They put it under a different case with a different number.”

The accusation was made during a tense hearing at the Santa Fe County District Courthouse, which prompted Judge Mary Marlowe Sommer to get down from the bench to examine the ammunition as a crime scene technician and lawyers for the defense and the prosecution looked on. She then sent the jury home for the weekend as she considers the issue.

The lead prosecutor in the case, Kari T. Morrissey, has blamed the movie’s armorer, Hannah Gutierrez-Reed, for bringing live rounds onto the set, which the armorer denied. Ms. Gutierrez-Reed was convicted of involuntary manslaughter for loading the live round into the gun that Mr. Baldwin was rehearsing with that day, and is currently serving 18 months in prison.