Well maybe Carver made threats to spill the beans . I'm sure he was under 24/7 wire taps and audio surveillance from days before the event took place .

All it takes is a slip up like saying " ya know I've got a lot of dirt on people in this town , or I know things that could destroy the Obama Administration . " Boom , Radio active poisoning , heart attack dart , HAARP stalking etc ..

Carver likely got greedy and wanted more hush money . That's what I think .