By CHRIS MELORE, US ASSISTANT SCIENCE EDITOR Published: 13:19 EDT, 2 April 2026 | Updated: 13:19 EDT, 2 April 2026 As the string of mysterious disappearances and deaths among America's scientists grows, a former FBI boss believes a sinister plot against the US could be unfolding.Chris Swecker, who was the assistant director in charge of the bureau's Criminal Investigative Division during his 24-year career, told the Daily Mail that foreign powers could be targeting citizens who have knowledge of US national security secrets.'The first thing you go to is it's potential espionage,' he said. 'Our scientists have been targeted for a long…