Discussion: Was It A Clean Kill?

Like I said yesterday, in my Shadowrun game on Wednesday night I killed a PC. To tell the honest truth, I one shotted him. 0 to Dead in one attack. The fun thing about the attack was that it was literally the first time I had a mage cast an offensive spell at a PC in the game. It was a mana ball as well. Not a stun ball or something non-lethal. No, the NPC was looking for blood. Also, while I'm continuing to tell the honest truth, I don't feel bad about the kill at all. To me it was perfectly justified, in character, and fair considering the rules in place in the game, the actions taken, and previous allowances made to players in similar but reversed situations. Of course, because it's me, the fact that I feel 100% justified makes me leary to accept that as an answer. So I figured today I'd present the case to you guys and see where you come down on the issue.

The Scene
To set the scene, the players are tracking a thief who stole a very valuable sword from a subsidiary of a very powerful Japanese corp. They have tracked the thief, a world famous magical thief, to an abandoned residential area that they believe to have been the thief's home when they were a kid. In the area they find 6 houses (3 on either side of a street in kind of a lego-block design layout). Each house has a strength 8 ward on it, and the astral perceiving  adept can sense the presence of spirits in the area.

Chain of Events
The players figure out which of the six houses the person they want is hiding in. They do this by staking the place out with mini-drones and seeing someone else bring in a duffel bag and two grocery bags into one of the houses. Two of the PCs go around the back of that house. Two of the PCs go to the front of the house. One of the PCs stays on the drones. And the two NPC muscle they have hold back to provide cover and extraction if needed.

Front Door
The PCs kick in the front door (it takes 3 attempts total) and get attacked by a dog. The dog goes out into the yard and howls. Both PCs and the 2 NPCs (in that order) take a shot at the dog with guns (3 pistols and 1 shotgun total). One of the PCs then goes over and tries to kick the dog. The other PC realizes the dog is trying to buy time and goes into the house. The dog follows, one of the drones dives down to have line of sight through the open doorway and disincorporates the dog spirit with a couple rounds from the attached LMG. Inside, the PC who ran inside goes through doors, finds a stairs down, sprints (rolls athletics for more distance) to go down the stairs as quickly as possible, runs into the NPC mage and takes a manaball for 13 physical damage (after soak) and drops to the ground. Two rounds later another PC fails the stabilization roll on the last possible round that it can happen, and the PC dies from their wounds.

Back Door
The PCs at the backdoor cue off of the sound of the front door being kicked and break the glass on the back door and kick in the plywood boarding keeping the door secure. It takes them a couple of attempts but they get in. They arrive in the house in time to see the dog running in after the other PC. These two split up to clear the house, one going towards the dog and the other going around a different way. The drone takes out the dog, and these two PCs arrive at the top of the stairs to the basement and see the first PC on the ground. They both leap down the stairs ready for a fight. A "are you alive" check is done to the PC finding that they are but they are fading. The same PC does a stablize check and only gets 1 of the 2 needed successes, so the roll fails and the PC dies from their wounds.

NPC Perspective
The NPC is hiding out in their old home while they get things together for the next action in their plan (can't go into too many details as the plot is still ongoing.) They are alerted by their wards/spells that a well armed group of people are moving in to their house, and they have someone with them in the house that they need to protect. Upstairs the front and back door are kicked in loudly. Gunshots are heard (a shotgun, some pistols, a heavy pistol, and good god, a machine gun.) The NPC has their companion open up the bolt hole while they cover the door. The bolt-door is opened just as someone comes running down the stairs with a gun in hand. The NPC casts the spell they've prepared for the first person coming down after them. The person, a gnome (looks like a 12 year old kid) drops and falls down the last two stairs seemingly dead. The NPC flees.

Justification
My justification for the lethal force used was simple. The NPC knew a large group was coming for them, and they didn't believe they were coming for a peaceful talk. The use of lethal force was a delaying measure, coupled with the fact that with the kind of theft they do - and the kind of world Shadowrun is - it is generally better to be killed resisting arrest than taken alive. Even still, the NPC was also doing this to protect something very valuable to them, which is the core part of what is going on.

The Die Roll
The real reason the spell was lethal was because of two factors. One, it was a force 10 spell. Two, the NPC rolled ridiculously well (and they did spend Edge to do so.) The force 10 is less a factor because the gnome 1/2'd the force and managed to soak 3 additional wounds with their willpower roll so the effective force on the spell was 2 + the NPC's successes. The NPC made their roll and got 11 successes, juicing the spell right back up.

So why the edge and why so much force?

Edge: The NPC is an important NPC (one I would normally deem "player level") and has been established to be a skilled magician for the acts they've taken/done. They know someone is coming after them, they need to stop at least the first person to buy time and they also expected their to be a mage with the group providing magical protection that they would have to over come..

Force: As I said, the NPC was expecting a mage to be on the attackers side, so they weren't expecting to be going only against a mundane's raw willpower in the resistance department. They also were expecting this to be a lethal fight and needed to buy time. Killing the first person down after them (if they had to exchange spells) did 2 things. One, the first person wouldn't be able to report where the bolt hole was. Two, the person coming down after would likely be more cautious/slower seeing the first person who rushed down on the floor.

Now, I can't give you the PC view of things as I'm unsure. But that is everything as objectively as I can give it. So, was it clean in your opinion? Or was there something I could have done better to make things go smoother?