New documentary 'A Compassionate Spy' reveals the crisis of conscience that led Manhattan Project physicist Ted Hall to spy for the Soviets, and how his spouse Joan kept his secret

Justice Department says it doesn't know whereabouts of 'Kremlin asset' Andrii Derkach, a Ukrainian politician who worked with Giuliani to dig up dirt on Biden

Peyman and Payam Kia allegedly worked together to pass information to Russian military intelligence for over a decade, with Peyman working for secret Swedish spy agency at the time

Bellingcat researchers say operative for Russia's military intelligence mingled with service members from US, European countries while posing as a cosmopolitan jewelry designer

Security agency also arrests Polish national suspected of collaborating with the group; Moscow dismisses claims, says it reserves the right to take retaliatory measures

New book 'Sleeper Agent' follows George Koval, a little-known US-born Russian spy posthumously honored by Putin - and possibly one of the 20th century's most influential operatives

Former KGB agent died in London in 2006 after drinking tea laced with radioactive material; UK charging 3rd suspect in 2018 nerve agent attack on ex-Russian agent Sergei Skripal

David S. suspected of sending documents to Russian intelligence; security specialist: 'A reminder of how much effort Russians put into trying to find out what West is up to'

Ilnur N., employed by an unnamed university, is believed to have met with Russian agents at least three times

Pair reportedly held diplomatic passports, were suspected -- but not charged -- of planning to spy on World Economic Forum being held this week in Swiss resort town