I don't know why not.
They have all the witness statements, they have a ton of physical evidence, blood, GSR, spent casing, bullet wounds, a body etc..
Considering the above, I cannot imagine what's holding up the completion of the investigation.
This shouldn't be too complex to determine what happened and if someone is providing inconsistent statements etc..
Details of the initial confrontation are not clear. Was the officer assaulted or was the officer not assaulted? It makes a difference. It doesn’t excuse, it makes a difference. If assaulted s/he was acting on adrenaline when shooting a fleeing assailant, if not... entirely different. It doesn’t excuse, it makes a difference.