A former Boeing manager suspected of spying for China is charging that a secret government warrant to search his house for evidence was riddled with errors, raising fresh concerns about the classified process used to carry out national security investigations.

The Justice Department in 2014 obtained a secret warrant seeking evidence that Keith Gartenlaub facilitated the theft of material on Boeing’s C-17 military transport plane. But Gartenlaub says documents he has reviewed strongly suggest the classified warrant — which neither he nor his lawyers have been allowed to see — was based on inaccurate assertions, including that he had access to the stolen data as part of his job at Boeing.

Six current and former Boeing employees said in interviews that government assertions about Gartenlaub and his role at the company, which were made in a separate FBI affidavit, were inaccurate, and raised serious questions about the case against him.

“I think a great injustice has been done,” said a Boeing colleague, an IT manager who has been with the company for decades, and who, like others interviewed, spoke on the condition of anonymity to avoid retribution. “I’ve known him for years and don’t believe any of the allegations against him are true. What happened has destroyed his life.”

Gartenlaub’s allegation follows the revelation in December by the Justice Department’s inspector general of significant errors in secret and highly sensitive government applications to wiretap a former Trump campaign aide, Carter Page.

The errors were so glaring that Inspector General Michael Horowitz is conducting a broad review of other applications made under the Foreign Intelligence Surveillance Act (FISA), which governs how and when federal agents can search and wiretap suspects in the United States in espionage and terrorism investigations. Horowitz is trying to determine if the missteps in the Page case are an exception or a sign of a wider breakdown in the process by which the government wields one of its most powerful, secret and intrusive investigative tools.

And now, Gartenlaub, who lost an appeal to have access to some of the evidence against him, wants Horowitz to scrutinize the secret warrant in his matter.

“I believe the FBI made unsubstantiated allegations to prove that I was an agent of a foreign power just because my wife is a Chinese American and I have family in China,” he said. “I was unable to defend myself because I can’t see their evidence. I understand national security. But we need to protect the constitutional rights of U.S. citizens as well.”

The Justice Department recently acknowledged that it lacked probable cause to seek two renewals of Page’s wiretap order. Gartenlaub and his attorneys say a scrub of his FISA application would probably yield a similar result.

“If we had had an opportunity to take that search warrant application and pick it apart the way Horowitz did with the Carter Page FISA, we could have defeated it,” said John Cline, a criminal defense lawyer and former “amicus curiae,” or special advocate, to the FISA court. “I’m convinced of that.”

Asked for comment, the Justice Department pointed to an October 2018 decision from the U.S. Court of Appeals for the 9th Circuit that concluded that “based upon our independent review of the classified record evidence,” the FISA was “supported by probable cause,” and that disclosure of the materials to Gartenlaub was not necessary to determine the legality of the search.

Cline, however, questioned just how “independent” the review could be if the court relied only on the government’s allegations. Just as the Justice Department has now acknowledged that it provided an incomplete and, in some cases, misleading picture of Page to the FISA court, Cline said he believes the appeals court received a similarly flawed view of Gartenlaub’s alleged affiliation to China.

“How could the 9th Circuit possibly know whether the FISA application contained material misstatements or omissions without permitting the defense to review the application and weigh in?” Cline said. “The court has no investigative power and very little knowledge of the case. Without an adversarial process, the court had to take the government’s word for its accuracy.”

Boeing and the FBI declined to comment.

Gartenlaub, whose wife is a naturalized U.S. citizen born in Shanghai, was suspected of being involved in the theft of designs of Boeing’s C-17 military transport plane for China. He was never charged with espionage, hacking — or any national security crime. Instead, he was convicted in 2015 on one count of possessing child pornography. He served 20 months in prison, was released in 2018, and now lives with his wife in Orange County, Calif. The porn images, which he contends he never saw, were found during the initial search of the house in old computer files that he says were copied from a computer used by numerous guests in a beach house he once rented. That FISA search warrant should never have been approved, he argues, and if it hadn’t, he would never have been prosecuted.

His case highlights a significant issue with national security prosecutions, and one that Congress may seek to address as a result of the inspector general’s report: The Fourth Amendment guarantees a defendant the right to challenge the veracity of the evidence used to obtain a search warrant or wiretap order. But, citing U.S. law, courts typically have not allowed disclosure in national security cases.

Though Gartenlaub was unable to see the FISA application, an affidavit that the FBI submitted seeking a criminal search warrant for his emails was made available to him as part of the prosecution.

“There could be substantially more information in the FISA,” said Daniel Grooms, a former federal prosecutor who is now a partner at Cooley LLP. “But it’s highly likely that, at a bare minimum, the material in the email affidavit would be in the FISA.”

The affidavit, Gartenlaub says, contains numerous misstatements and omissions. It was submitted in June 2013 by FBI special agent Wesley K. Harris, who cited a Wired magazine article stating that similarities between the Chinese-built Y-20 and the C-17 may be attributed to a “spy working at Boeing.”

Harris asserted that Gartenlaub was the only Boeing employee with “the combination of access to the C-17 data, knowledge of the computer network and systems, suspicious behavior and concerns by security personnel who worked with him, and connections and travel to China” that give probable cause to believe evidence of crimes.

The C-17 breach, according to government records in a related case, took place in 2009 and 2010. Yet, according to colleagues and employment records that Gartenlaub shared with The Washington Post, Gartenlaub, who was hired in 1998, had no position involving the C-17 until April 2011.

In 2011, Gartenlaub became an information technology manager in charge of a C-17 engineering support team in Long Beach, Calif. He oversaw developers who provided software for the engineers designing the cargo plane.

A crucial contention by Harris is that Gartenlaub in 2012 became “the nationwide Unix military administrator for Boeing,” which would “permit him access to Unix [computer] servers for all military projects, including the Unix server that houses the C-17 files.”

But current and former employees said no such position exists. “Nothing even close,” said a former software developer who retired in January. “No one has Unix nationwide server access at Boeing.”

Another Boeing colleague said Gartenlaub was not a Unix administrator at all while working on the C-17 support program. “He had no access to any of the actual software systems,” said the colleague, a software engineer who worked with Gartenlaub. “He was purely management. He didn’t have the technical knowledge or interest or need to actually access the software systems we maintained.”

Added the engineer, who checked Boeing records: “There is no trace of Keith ever having access to C-17 systems, period.”

In fact, the job Gartenlaub was named to in September 2012 was “manager of environment management,” according to an email announcement viewed by The Post.

Many of Gartenlaub’s colleagues were puzzled by the allegation that he was linked to the breach. “We had always heard that there was a full-fledged Chinese version of the C-17 even before he came over as manager,” said a second former Long Beach colleague. The Chinese would have needed to get the data long before Gartenlaub arrived, the colleague said.

In July 2014, a few months after the FISA search of Gartenlaub’s house, a Chinese businessman in Canada was arrested on charges of conspiring with Chinese military officers who hacked Boeing computers to steal military technical data — including data related to the C-17. The businessman, Su Bin, who consented to be brought to the United States, was convicted in March 2016 and sentenced to 46 months in prison.

Su’s criminal complaint listed the types of data that he directed the Chinese hackers to look for. They included files such as “C-17 station guide.pdf,” “C-17A-brochure.pdf” and “C-17 Hangar Requirements.”

An IT manager who worked with Gartenlaub reviewed the list of items and said this was not material Gartenlaub had access to. That data was used by the product support division — a different entity than the division Gartenlaub was in.

Brant Reed, a former Boeing senior manager of product data management who was Gartenlaub’s boss, agreed. “It’s rare that we keep our engineering data in pdf format,’’ he said. “It’s usually native format.”

There are other allegations in the warrant application that Gartenlaub contests.

Harris noted deposits into the Gartenlaubs’ bank account totaling $116,500 that he alleged were “compensation” for assisting in the theft of C-17 data.

Gartenlaub said the payments all have innocent explanations. More than half consisted of checks for such items as unemployment benefits and medical reimbursements, he said. A $25,000 wire transfer from a bank in China to the couple’s Bank of America account was in fact a returned transfer from the U.S. bank because he had inadvertently listed an incorrect routing number when sending money to be used as a down payment on an apartment in Shanghai that his wife was seeking to buy, he said.

To date, there has been only one instance in which a judge ordered disclosure of FISA material — in a 2014 terrorism case. An appeals court overturned the order. Still, in her concurring opinion, Judge Ilana Rovner of the U.S. Court of Appeals for the 7th Circuit in Chicago noted the “conundrum” faced by defendants in these cases. A defendant cannot make a “viable” challenge “without access to the FISA application,” she wrote. And the court, she said, “cannot, for the most part, independently evaluate the accuracy of that application on its own without the defendant’s knowledge of the underlying facts.”

Correction: A previous version of this article incorrectly said that Gartenlaub owned the beach house where he says a computer was used by numerous guests. He rented the beach house.