Central intelligence agencies intercepted communications after 52-year-old Captain Babu allegedly shared equipment and defence details with an unknown handler.
Court filings claim Abdulrahman Alfozan discussed artificial intelligence work with a royal family member before his arrest for planting a listening device.
A Southern California real estate agent was stopped at the boarding gate for a flight to Shanghai after allegedly filming the Seattle home of Ting-Yu Lai.
The State Department has approved the $24.3bn deal, but intelligence reports warn Beijing could gain access to America's crown-jewel military technology.
DNA left on a remote control antenna linked a Russian intelligence officer and his Belarusian accomplice to a failed explosives attack near a Ukrainian transport jet.
