This is an interesting case (see LVRJ article). On Sunday night, 4/5 around 6 PM, an LVMPD helicopter saw a motorcycle "acting very suspicious" in a parking lot near Sahara and Decatur. The drive then fled the area and crashed near Bonanza. The rider fled into a nearby condo complex.
The armed citizen, who holds a concealed firearm permit, was outside to see why the helicopter was overhead. At this point, the suspect ran into the armed citizen. The armed citizen told the suspect to stop, but the suspect fled, so the citizen followed, intending to call police.
At some point, the motorcyclist turned around, brandished a knife, and turned back towards the armed citizen, at which point the citizen fired two rounds in self-defense. The citizen also retrieved a first aid kid and started to administer first aid before officers and medics took over. The suspect died at the scene.
One of the interesting factors here is that the citizen got a first aid kit (we don't know what kind) and began first aid. Kind of hard to argue something like the Zimmerman case when the innocent shooter tries to save the life of the wounded (and dead/dying) suspect. This also was probably captured on video from the air. It will be interesting to see if Metro releases video footage from the helicopter when the DA's investigation is complete.
It's always important to note that you are not the police and shouldn't try to detain or follow someone who is running from the police. Sure, it worked out this time, but it doesn't always. However, this is as near a perfect defensive gun use there is if, if you can have one at all.