A former US army intelligence officer has been charged with attempting to provide classified defence information to the Chinese security services during the outbreak of the Covid-19 pandemic – including some listed in a Microsoft Word document titled “Important Information to Share with Chinese Government”.

Authorities on Friday arrested former sergeant Joseph Daniel Schmidt, 29, at San Francisco international airport as he arrived from Hong Kong, where he had been living since March 2020, the Justice Department said. A federal grand jury in Seattle returned an indictment on Wednesday charging him with retention and attempted delivery of national defence information.

A public defender assigned to represented Schmidt at a brief appearance at US district court in San Francisco on Friday pending his transfer to Washington state did not immediately return an email seeking comment. US district court records in Seattle did not list an attorney representing Schmidt on the charges, and neither the US attorney’s office nor the federal public defender’s office had information about whether he had a lawyer, representatives said.

An FBI declaration filed in the case quoted Schmidt as telling his sister in an email that he left the US because he disagreed with unspecified aspects of American policy.

“I don’t talk about it often, but I learned some really terrible things about the American government while I was working in the army, and I no longer feel safe living in America or like I want to support the American government,” he was quoted as writing.

Schmidt spent five years in active duty in the army, where he was primarily assigned to the 109th military intelligence battalion at joint base Lewis-McChord in Washington state, according to a declaration filed in US district court by FBI special agent Brandon Tower. He eventually became a team leader on a human intelligence squad and had access to secret and top secret defence information, Tower wrote.

Schmidt left active duty in January 2020 and travelled the next month to Istanbul, where he sent an email to the Chinese consulate trying to set up a meeting, Tower wrote.

“I am a United States citizen looking to move to China,” the email said, according to the declaration. “I also am trying to share information I learned during my career as an interrogator with the Chinese government. I have a current top secret clearance, and would like to talk to someone from the Government to share this information with you if that is possible … I would like to go over the details with you in person if possible, as I am concerned with discussing this over email.”

It was the first of several attempts to share information with the People’s Republic of China, Tower wrote. Two days later, he drafted a Word document titled “Important Information to Share with Chinese Government” that included classified information related to national defence. Investigators recovered it from his Apple iCloud account, the declaration said.

After returning to the US from Turkey in March 2020, he left a few days later for Hong Kong, where he had been living ever since, the declaration said.

Over the next few months, Tower wrote, Schmidt emailed two state-owned enterprises in China, including a subsidiary of the China Aerospace Science and Industry Corporation Limited that has produced intelligence-gathering software tools.

He offered to provide an encryption key he had retained for accessing the army’s classified information network and related databases, known as the secret internet protocol router network, or SIPR, Tower wrote, and he suggested it could be reverse-engineered to help China access the network.

“It is a very rare card to find outside of the intelligence community, and if used properly, it can improve China’s ability to access the SIPR network,” the declaration quoted him as writing.

The declaration did not describe any response from the state-owned enterprises or China’s security services.

The charges carry up to 10 years in prison and a $250,000 fine.