The judge overseeing Alec Baldwin’s involuntary manslaughter trial dismissed the case on Friday after the actor’s lawyers accused the state of withholding evidence that could have been relevant to how live ammunition reached the set of the “Rust” movie, leading to the fatal shooting of its cinematographer.

After Mr. Baldwin’s lawyers called for dismissal of the case, Judge Mary Marlowe Sommer sent the jury home for the weekend, and the prosecution and defense began questioning witnesses who may have insight into the new evidence: rounds of ammunition that were turned in to the police several months ago.

On Thursday, the defense revealed while questioning a crime scene technician that a retired police officer had turned in the rounds, which he thought to be linked to the “Rust” set.

Judge Sommer ordered that the rounds be brought into the courtroom, and she took the unusual step of getting up from her bench and examining the rounds herself.

The case revolves around the events of Oct. 21, 2021, when the gun Mr. Baldwin was rehearsing with discharged a live bullet that killed the cinematographer, Halyna Hutchins, and wounded the movie’s director. The weapon was supposed to have been loaded with inert rounds that could not fire.

The trial’s first three witnesses were members of law enforcement who responded to the fatal shooting. The jury saw footage of the chaotic moments when an on-set medic was tending to Ms. Hutchins.