A Massachusetts prosecutor on Wednesday asked for charges to be dropped against actor Kevin Spacey, who had been accused of groping the son of a former Boston TV news anchor at a Nantucket bar three years ago.

Cape & Islands District Attorney Michael O’Keefe cited the “unavailability of the complaining witness” in filing for dismissal in Nantucket District Court.

The case against Spacey appeared to suffer a fatal blow last week when Spacey’s accuser invoked his Fifth Amendment rights after being questioned about his role in the deleting of text messages from a phone key to the case.

Spacey’s defense had demanded to examine the accuser’s cell phone that he had in the early morning hours of July 8, 2016, when the alleged incident happened at the Club Car restaurant and bar in Nantucket.

On the witness stand, the accuser said he had not altered or deleted any potential evidence off that iPhone he had in 2016. But when Spacey’s lawyer, Alan Jackson, reminded him it is a felony to alter evidence, the court took a break and then the young man told Nantucket District Court Judge Thomas Barrett — through a public defender assigned on the spot — he’d invoke his right against self-incrimination on the phone issue.

The young man and his family met with prosecutors this past Sunday and he decided not to waive his right to invoke the fifth.

“The complaining witness was informed that if he chose to continue to invoke his Fifth Amendment right, the case would not be able to go forward,” according to a statement issued by prosecutors.

“After a further period of reflection privately with his lawyer, the complaining witness elected not to waive his right under the Fifth Amendment.”

In theory, prosecutors could have granted the accuser immunity for testimony — but that would make a conviction virtually impossible with such a tainted witness.

“A grant of immunity compromises the witness to a degree which, in a case where the credibility of the witness is paramount, makes the further prosecution untenable,” according to prosecutors.

In court last week, Jackson said the case against his client was dead.

“This entire case is completely compromised. He is the sole witness,” Jackson said. “This case needs to be dismissed, and I believe it needs to be dismissed today.”

Judge Barrett seemed to agree, but put the matter off so prosecutors could discuss their next move. He ordered both sides back to court on July 31.