Who is Paul Whelan? Prisoner swap puts focus on Marine still held in Russia

Read MorePaul Whelan, a 52-year-old retired U.S. Marine Corps veteran, has been imprisoned in Russia on espionage charges since his arrest at the end of 2018.Paul Whelan, a 52-year-old retired U.S. Marine Corps veteran, has been imprisoned in Russia on espionage charges since his arrest at the end of 2018.