Just playing the Devil's Advocate here...
But, in some cases, it's better for the officer to have the case go to trial and have that court find him justified in deadly force than it is for Grand Jury to return a no-bill.
Even if a No-Bill is returned, he could be indicted at any point afterward.
If it goes to trial, the Double Jeopardy rule of law protects him. (Except when the Feds demand a civil rights violation prosecution)
The thought crossed my mind more than once... let em go to trial and show the evidence says he is in the right.....
