NANTUCKET, Mass.—The man accusing Kevin Spacey of sexual assault refused to testify at a pre-trial hearing in Massachusetts on Monday, invoking his Fifth Amendment right and casting doubt on whether the case would proceed to trial.

Spacey, 59, is charged with felony indecent assault and battery for allegedly groping an 18-year-old busboy at a local bar in 2016. Monday’s hearing concerned the whereabouts of the accuser’s phone that contains evidence about the alleged assault.

In a hearing that packed the tiny Nantucket courtroom, the accuser answered questions about text messages he sent to friends during the alleged encounter. The defense claims potentially exculpatory texts are missing from screenshots of the conversations that the accuser later sent to police.

The accuser said Monday that he did not delete any of the messages. But when Spacey’s attorney, Alan Jackson, advised him that tampering evidence was a felony, the former busboy asserted his right against self-incrimination fifth and declined to testify in the rest of the hearing.

Jackson then moved to dismiss the case completely.

“This entire case is completely compromised,” the defense attorney said. “[The accuser] is the sole witness who can establish the circumstances of this allegation on the night in question.”

Judge Thomas Barrett denied Jackson’s motion to immediately dismiss, but added later, “I don’t know what’s going to happen with [the accuser]—whether the case is going to continue or collapse.”

The case stems from allegations brought in 2017 by the accuser’s mother, former Boston TV news anchor Heather Unruh, after dozens of people publicly accused Spacey of sexual misconduct.

The accuser, who has asked not to be named, told police in late Oct. 2017 that Spacey bought him several drinks and began flirting with him after his shift at the Club Car bar in 2016. He says Spacey unzipped his pants and rubbed his penis for about three minutes, while the accuser texted his friends for help. The accuser later sent screenshots of these texts to police.

Judge Barrett has ruled that the defense can inspect the phone for any texts missing from the screenshots, but the accuser’s family has so far failed to produce it. The family says they have not seen the phone since they turned it over to police in Nov. 2017. The police say they returned it that same month.

On Monday, Jackson read aloud several texts he said were recovered from the phone during a police analysis. In one, the accuser’s girlfriend at the time wrote, “I can’t really tell if you’re kidding and I’m violently confused.” In another, she added, “Holy shit, slowly back away.” Neither messages appear in the screenshots the accuser initially submitted to the police.

After the accuser declined to testify at the hearing, Jackson turned to his mother, Unruh. The former television anchor had previously told police she deleted evidence of her son’s “frat boy activities” from the phone before turning it over to them.

In the hearing, Unruh held firm to her position that she had not deleted anything related to the incident in question, despite persistent questioning from Jackson about her son’s drinking habits and language.

But Jackson seemed to insinuate that even this was enough to charge Unruh—who tearfully waived her right to plead the fifth—with tampering with evidence.

“You don't get to pick, Ms. Unruh,” he said. “What’s deleted and not deleted and is not your choice.”

“I’m beginning to understand that,” she replied.

The accuser’s father, visibly upset by the day’s proceedings, also answered questions from the defense. He repeatedly told Jackson he thought the questioning had gone “way too far” and attempted to turn the conversation back to the alleged assault. When the judge threatened to hold him in contempt, he rolled his eyes and shook his head.

The accuser's family dropped a civil case against Spacey that made many of the same claims last week, “because of the emotional roller coaster my client is on,” their attorney said Monday. No settlement was reached, according to Unruh.

A case status hearing is set for July 31, but Jackson said he “clearly” planned to file a motion to dismiss before then.

More than a dozen people have accused Spacey of sexual harassment or assault since 2017, when Broadway star Anthony Rapp accused the actor of sexual assaulting him decades ago, when Rapp was 14. Spacey claims to have no memory of the alleged incident, but was dismissed from his hit Netflix series House of Cards. The case is one of the few criminal prosecutions to come from the #MeToo movement.