An odd report via Twitter, from an untested source that relies on a local Miami paper and it starts with:
According to the Miami Herald, Brandon Russell, Arthurs’ roommate, was in possession of multiple materials meant to build explosives, including a lethal bomb-making chemical named hexamethane triperoxide diamine. FBI and Tampa Police Department officers found the materials in Russell’s garage.
While in his bedroom, devices used by police bomb technicians alerted to the presence of radiation sources — thorium and americium.
Link:http://www.rawstory.com/2017/05/fbi-...ive-materials/

The local paper's report:http://www.miamiherald.com/news/loca...151953257.html

Leaving aside that Russell was serving in the National Guard; he lived with an extremist who was building IEDs possibly with radioactive components.