If it's a weapon the obvious first guess would be sonic, rather than some other directed energy weapon that produces a sonic effect indirectly.

Of course the US government has wave-based weapons - she literally has a photo of one in her rebuttal - but microwave weapons are not subtle. You could use one as a weapon of torture, but as an assassination tool you'd have to amp up the power to the point where you're either burning a hole through someone or cooking them alive.