Innocent and exonerated mean the same thing. Not guilty is a chasm away from those two concepts.Grey area word salad.
If they are not found guilty of the charges against them, they are innocent, or exonerated of wrong doing. Call it what you like.
This is not gray area word salad. That chasm is exactly where the problem lies. Police can and do get away with morally unlawful killings because the standard for reasonable doubt applied in police shooting criminal cases is extremely high.