Watching it closely, it appears that the dropping of the stun gun may not have much significance. In the beginning of the video it drops to the ground, so it very well may have been that the victim was trying to wrestle it away. But, it is clear that the suspect is simply running away when shot in the back, so don't think that will be a valid excuse. He goes back, picks it up and then drops it next to the suspect. Leaving were it was would have been almost or more effective. He then appears to pick it up later and stick in back in the holster, so if it was a clear plant job, it seems he would have just left it there.

I think he could get away with manslaughter, but when he handcuffs him and does not immediately attempt to help the suspect, it could turn into a full blown murder charge. If it is determined he was planting evidence, then he will most likely get a straight murder charge, possible even a 1st degree charge.

Of note also, is the sad realization that the black officer on the scene appears to be the one who seems most concerned with the suspect, but even he does not bother to remove the handcuffs from the clearly unconscious and dying victim.

I would love a dream world where the video did not come out until after the initial determination from the police department. It could do wonders in showing how biased the system is.