An oppressive government entity roughly 70 years in the future has access to elite--albeit experimental--technology. One such technology is a brain chip that allows its soldiers to control simple machines. It's fairly limited to just an on/off process, like we see in some technology today (I think of games like Mindflex).
If nanobots were introduced to a victim's bloodstream, could an on/off process be able to contract nanobots in areas of the body to stop a victim's heart, deflate his lungs, or rupture a spleen? Remember, it's only an on/off process, so they wouldn't necessarily be able to control the nanobots to specific places or do specific things. Only simple actions like "contract/relax," etc.