There's more evidence then has been seen and heard. A Grand Jury most likely won't hear all of it. The attorneys generally reveal as much evidence as is necessary to secure a true bill. Jurors are instructed that if through deliberation they feel compelled to no bill, to have the foreperson ask for more evidence, before no billing. They have the power of subpoena, and can ask for whatever they wish. Also, their bar is much lower than the trial jury, they need only find probable cause whereas the latter must find beyond reasonable doubt.
Killing one person is murder, killing 100,000 is foreign policy