I'm not an expert in US Law but I don't think police officers are allowed to kill individuals who are surrendering to them and who pose no threat to their lives. Perhaps you know better?
Again, that's a judgement made in hindsight.
The officer was on high alert & had 1 second (8/10ths of a second according to CNN) to establish if the subject was no longer armed & if the subject was in fact surrendering as they turned toward him.
Murder in the 1st degree wouldn't stick imo, he could quite possibly claim self defence. Plus he rendered aid after firing the shot, so proving intent to kill would be difficult imo.
Murder 2, I'm not sure about. "These charges stem from instances where someone knowingly and purposefully killed someone but did so with factors that impacted their state of mind at the time of the murder."
Manslaughter "Manslaughter includes actions that result in the death of another person through reckless behavior or extreme negligence on the offender’s behalf."
I don't think the officers actions can be described as reckless or extremely negligent, when viewed in the moment as oppose to after the event
https://www.mencinilaw.com/itasca-immigration-criminal-defense-lawyer/what-are-the-different-levels-of-homicide-charges-in-illinois