Did he actually do it though? The police at the scene did not fingerprint Wilson's gun and then give somewhat conflicting account about whether or not there was a struggle. The whole scenario sounds like they worked out an official scenario and had to change a few details, but had to pretend to be grossly incompetent at the grand jury trial.
source:
https://www.documentcloud.org/documents/1370672-grand-jury-volume-3.html
Wilson did not shoot and kill Brown from inside of his car. I know you're aware of that, so this statement of yours is remarkably dishonest. His pepper spray could have been easily used while they were both out in the open on the street.
Wilson also carried a night stick. Less effective and more risky, but it's still an option.
However Wilson
choose not to carry a taser. It is a standard piece of equipment for Ferguson PD. Wilson choose not to carry it. Just like the police department choose not to install the dashboard cameras it had on hand. Strange that. I wonder why they kept choosing not to use equipment like that?
Almost all forcible felonies carry the risk of bodily harm, usually with the aid of a weapon in case of things like robbery (which would make a reasonble fear of great bodily harm or death). But someone could be convicted of felony robbery for threatening to cause non-great bodily harm in a robbery, so I'll concede the point.
However, with regards to this particular case, Wilson claimed that he feared for his life. Which is what I was getting at, the same criteria applies for a cop who "fears for his life" as for a regular joe.