The problem is, the good guy closes to the bad guy while he is prostrate on the ground, and plugs him 3 times at close range when there is no apparent deadly threat present. Then, he shoots him again when he leans over to pick up the toy gun.

Personally, I've only got a problem with the last shot. Shooting him when he was on the ground was - again, in my opinion - fine, since I view it as all part of the same instance. You've got adrenaline pumping, time is moving weird, you're closing on someone who is still armed. Maybe those shots weren't perfect, but I think they're easily justifiable.

That last one...oof. Looks bad, and it's a much harder argument to make for that one, considering he's been disarmed, and you're so close; you could easily control him at that point without a gun at all...he's been shot seven times, is lying on the floor, and you can be on top of him in an instant.

That said, he's probably/hopefully still legally fine. You can make some of the same arguments about adrenaline and heat of the moment, and the last shot will hopefully get lumped in with the others as justified. But, yeah, pretty sketch on that last one, gotta say.