A U.S. Navy nuclear engineer pleaded guilty on Monday to a charge that he tried to sell some of America’s most closely guarded submarine secrets to a foreign country, in an agreement that is likely to send him to prison for 12 years or more.
The engineer, Jonathan Toebbe, was arrested in October with his wife, Diana Toebbe, and both had initially pleaded not guilty to one count of conspiracy to communicate restricted data and two counts of communication of restricted data. F.B.I. agents laid out a detailed account of how the Toebbes wrote to a foreign country offering to sell submarine nuclear reactor secrets in exchange for cryptocurrency.
Under the plea agreement, entered in federal court in Martinsburg, W.Va., Mr. Toebbe pleaded guilty to a single charge of conspiracy to communicate restricted data. Ms. Toebbe was not part of the plea agreement.
But as part of the plea agreement, Mr. Toebbe admitted that his wife was part of the conspiracy to sell the secrets and served as a lookout when he deposited information at the dead drops set up by undercover F.B.I. agents.
In the agreement, he acknowledged that he sent the initial message to the foreign country, which has not been identified, and then communicated with an undercover F.B.I. officer. But, in the agreement, Mr. Toebbe said his wife “committed multiple overt acts in furtherance of the conspiracy.”
As part of the deal, Mr. Toebbe will help the government recover the cryptocurrency that undercover F.B.I. agents paid him, as well as the classified information he said he had never turned over.
Mr. Toebbe had faced the possibility of life in prison, but under terms of the deal will instead face about 12 to 17 and a half years in prison. Such a wide range, former officials said, could signal that the government wants to see what sort of further cooperation Mr. Toebbe will give investigators.
The case received broad attention, raising questions of how a couple in a suburban home in Annapolis, Md., could become ensnared in an international spy plot. Some of the details of the case seemed to be out of a bad novel. The F.B.I. accused Mr. Toebbe of hiding the memory cards he left at the dead drops in a peanut butter sandwich, a gum package and a Band-Aid wrapper.
Other aspects of the case felt like an awkward clash of international intrigue and the bland stress of suburban life, with the accused would-be suburban spies hunting for a babysitter so they could make it to a dead drop in West Virginia.
A key question is how Mr. Toebbe’s plea deal will affect the proceedings against his wife, a former teacher at a private school in Annapolis.
Ms. Toebbe was not part of the plea negotiations involving her husband.
To a degree, the plea deal put Mr. Toebbe alone at the heart of the plot. He acknowledged taking the major steps to sell the nuclear secrets to the foreign country and communicating with the person who turned out to be an undercover F.B.I. agent.
But he also said Ms. Toebbe took part in the conspiracy.
The statement was at odds with what Mr. Toebbe had said in jailhouse phone calls in November. In one call, outlined in one of Ms. Toebbe’s filings seeking release on bond, Mr. Toebbe told his son that she did not commit a crime. In another call, to his father, Mr. Toebbe said he would provide evidence that “will help clear Diana’s name.”
His admission of at least a limited role in the conspiracy set the stage for the prospect of Mr. Toebbe testifying against his wife, should her case move to trial.
While Mr. Toebbe had done little to contest his pretrial detention or the charges against him, Ms. Toebbe’s lawyers have mounted a defense that she knew nothing of the plot to steal secrets. While she had gone to the dead drops, she did not know of the scheme, her lawyers said.
The charges against Ms. Toebbe took her colleagues and former students by surprise, and many began wondering if the dissatisfaction she expressed about American politics in the classroom had taken a more sinister turn.
In her initial detention hearing, her lawyer said that while she did complain about former President Donald J. Trump, she did not betray her country.
But officials briefed on the investigation had portrayed Ms. Toebbe as being involved in the plot to sell the secrets her husband had meticulously stolen from the Navy over many years.
Still, despite repeated attempts to have a court end her pretrial detention, a magistrate judge had refused, ordering her held without bail. The judge supervising the case has not held a hearing to review the decision to keep Ms. Toebbe detained.
While Mr. Toebbe’s plea agreement outlines a potentially small role for his wife — serving as a lookout — it could be enough to set her up for a significant sentence.
“If those are the facts, it’d be really hard to let someone like that, no matter how sympathetic as a mother of young children, not face serious jail time,” said Michael Atkinson, a former inspector general for the intelligence community. “It’s just such a serious crime.”
Mr. Atkinson, now a partner at the law firm Crowell & Moring, said Ms. Toebbe’s case would set a precedent, and the government would be conscious of that when pursuing a plea deal with her.
“If she ends up getting minimal jail time, that’s not a very good precedent for the government given the risk to national security and what she apparently knew about the underlying conspiracy,” he said.
A sentence of more than a dozen years for Mr. Toebbe would be in line with similar cases involving U.S. officials who thought they were selling secrets overseas but instead were caught by undercover F.B.I. agents.
Mr. Toebbe had relatively little leverage in his plea agreement, but the government admitted it had not recovered the cryptocurrency it had paid him and had not found where he hid the rest of the documents he had taken.
While Mr. Toebbe claimed to undercover F.B.I. officers to have thousands of pages of classified documents relating to the nuclear reactors on Virginia-class attack submarines, he appears to have stolen them slowly, taking a few pages at a time out of his classified workplace.
In recent years, Mr. Toebbe worked in the Washington Navy Yard in a department that designs nuclear reactors for the submarines. Navy officials said they worked to tighten security after the initial charges against Mr. Toebbe.