A Marine vet fatally subdued a screaming man on a NYC subway. Now, a secret video has emerged — but there’s a catch.

The couple had been visiting New York City — from “Europe, someplace,” as the judge described it on Monday — when they filmed Penny grappling on the car’s grimy floor with victim Jordan Neely.

The tragedy roiled a post-pandemic city that was struggling, with mixed success, to reduce crime and convince tourists and commuters to return to its streets, restaurants, theaters, and offices.

Penny’s lawyers now believe the husband and wife’s footage could be among their best evidence in the divisive case, potentially shedding more light on Neely’s actions in the minutes before his death and bolstering their defense that the killing was justified.

However, the couple has refused to turn the footage over to prosecutors. They have also refused to testify before the grand jury that indicted Penny or the trial jury that is due to be picked beginning on October 21.

Since recording the video on May 1, 2023, the husband and wife “have gone back to their home, which apparently is in Europe, someplace,” New York Supreme Court Justice Maxwell Wiley said Monday, according to a transcript of an unannounced pretrial hearing.

“They have so far refused to share the video they took,” the judge continued. “They refused to share it with the DA, or with anybody else, and they are so far refusing to come back to testify.”

To date, the judge noted, the pair has only agreed to meet with the DA a few times, via video. The judge called those meetings “ongoing.”

Prosecutors have turned their notes from those meetings over to defense lawyers, who on Monday expressed a great eagerness to know the husband and wife’s identities and the video’s contents.

“Not only is it probative, I mean, it is incredibly favorable to the defense, or at least certain parts of it,” defense lawyer Thomas Kenniff said of the notes of these meetings, speaking to the judge Monday.

“Maybe more probative than any testimony of the issues that are going to be at issue in this trial.”

The defense noted that because the husband and wife live outside the United States, their testimony and video may be impervious to subpoenas from either side.

Still, Kenniff suggested that, based on the DA’s notes, the couple’s footage and testimony are so good for the defense that prosecutors are making less than a good-faith effort to secure either.

“If we are at the same point a few weeks from now, then that’s, I think, a very serious issue,” Kenniff said, warning that his client’s right to present a defense was being compromised.

Prosecutors have possession of at least two other eye-witness videos, according to court filings, but both start after Penny has begun to choke Neely.

The next hearing in the case is set for October 3.

Penny, of Long Island, remains free on $100,000 cash bail, and his online defense fund has raised $3 million.

He has pleaded not guilty to an indictment that alleges he was reckless or at least negligent when he used excessive force on Neely, continuing to choke him for nearly a minute after the prone man had stopped moving.

Neely was a homeless street performer and Michael Jackson impersonator. He had schizophrenia, multiple assault arrests, and a history of using K2, a powerful synthetic marijuana, according to court papers filed by both the prosecution and the defense.

Prosecutors have noted that, according to multiple eye-witnesses, Neely was verbally threatening passengers at the time Penny jumped him. In a court filing on Monday, prosecutors conceded that there was a “synthetic cannabinoid present in his blood at autopsy.”

Still, “the defense should not be permitted to introduce damaging background information regarding the victim’s character and history,” lead prosecutor Dafna Yoran wrote in the filing.

“The only reason to do so is to influence the jury to devalue Mr. Neely’s life,” Yoran wrote.

Kenniff and a spokesman for the district attorney’s office declined to comment on this story.