Jareh Sebastian Dalke disabled the location tracking system on his car then drove north from his home in Colorado Springs to Denver's Union Station. He made sure to leave without his phone.
The 31-year-old former US National Security Agency (NSA) employee parked several blocks away, walking to the train station with a laptop, a memory card, a gun and a note with handwritten instructions for his clandestine mission.
Dalke had spent several months communicating via email and transmitting top secret, classified information to someone he believed was a Russian foreign agent.
He was preparing to send more files after receiving instructions on how to access a secure connection at the station.
On the day of his mission, in September 2022, Dalke opened his laptop and emailed five files. One was a letter written in Russian, according to court documents.
"My friends!" it began. "I am very happy to finally provide this information to you... I look forward to our friendship and shared benefit. Please let me know if there are desired documents to find and I will try when I return to my main office."
However, his "Russian" contact was in fact an undercover US Federal Bureau of Investigation (FBI) agent.
FBI agents surrounded him moments after he sent the files.
Dalke on Monday received a nearly 22-year prison sentence for attempted espionage after sharing classified information.
He pleaded guilty last year to six counts of transmitting national defence information to a foreign agent.
"This defendant, who had sworn an oath to defend our country, believed he was selling classified national security information to a Russian agent, when in fact, he was outing himself to the FBI," said Attorney General Merrick Garland in a statement.
Dalke, who worked as an information systems security designer at the NSA, admitted to using an encrypted email account to share excerpts of classified documents. He held a top secret security clearance and signed a lifetime binding non-disclosure agreement as part of his role.
He obtained the documents while working at the agency.
Dalke started working at the NSA in June 2022. He worked for less than a month before requesting a nine-month leave of absence to help a family member with a medical condition, according to court documents. He was denied the leave and later submitted a letter of resignation.
He later re-applied for a position and accepted an offer of re-employment with the agency around the same time as his arrest in Denver.
Dalke asked for $85,000 (£67,953) through cryptocurrency from the undercover agent in return for the excerpts and promised to share more information in the future, according to court documents.
He admitted to wilfully transmitting the files with the intent that the information could benefit Russia, according to the US Department of Justice. He also admitted to using an encrypted email to demonstrate his "legitimate access and willingness to share" classified information with an individual who he believed was a Russian agent.
The classified documents included details related to foreign targeting of US systems and information on cyber operations, according to court documents.
In one of his emails transmitting files, Dalke wrote the excerpts were a "small sample of what is possible".
