FBI Tunnel Source Location Under Russian Embassy - Best Candidate

In 1980, Soviet officials announced eavesdropping devices had been discovered within their embassy compound. It is believed Robert P. Hanssen, FBI double-agent, revealed to the Soviets that a tunnel had been built by the FBI and CIA under their Mount Alto site. The tunnel is reported to have been cemented up but the source location has remained unconfirmed. Continued investigation and recent construction has exposed the most likely candidate to the unknown source location of the tunnel.