New developments into the case pointing to an unjustified shooting.  I originally thought that the deputy may have been in a side headlock, which could be lethal force, with the deputy drawing
and shooting into the guys back.  Shooting at a downward angle would be very awkward, but still possible.

Also what could've possibly happened is the deputy squirmed out of a headlock, moved back, drew his gun, then shot him.  Self defense would be questionable at that point, but worse case would be manslaughter or assault, not murder.

Also the report confirms that the guy was 5'3" and 117lbs with a possible leg disability.  That's pretty lightweight to go against a trained deputy.

Police reclassify Capitol shooting as murder case

"shows that Espejo was shot at close range from a downward angle, with the entry wound located in his upper back, 12 inches below the top of his head."

https://www.staradvertiser.com/2019/06/29/hawaii-news/police-reclassify-capitol-shooting-as-murder-case/?HSA=fed0831094ef81e20fa8b0f3e3976250a3ef1409