In most jurisdictions you are going to be responsible for the result on something like that, regardless of intent. So, was it first or second degree murder, murder or manslaughter?
The thing with booby traps/IED's is that they don't care what or who sets them off. In addition, homemade jobs tend to be HIGHLY unstable and unpredictable. Booby traps are never the right answer! (At least when you aren't chasing Osama through Tora Bora). It simply is not worth the risk, legally and physically.
Depends on what load of shot he used. Rock salt, say, or birdshot would be one thing.
If he's putting 00 buckshot in the shotgun, well, how can he say he "wasn't intending to kill anyone"?
As I understand it, he DID use a light load of some kind. The issue was, he set up the gun so that it would shoot a grown adult in the stomach, injuring, but not killing them. (It had to have been bird shot, or rock salt, or something...) BUT, when a small child approached the door, the small child took it in the face. The guy's main argument was that he did not have the requisite "intent" for murder, because the trap was not "designed" to kill anyone.
The jury (and the appeals court) did not buy it. They said that, if the guy had thought about it, it was conceivable that a small child could get shot in the face. Thus, the guy "knew or should have known" that death or SBI was likely to occur.
Since we are talking about booby traps I have a story to share as well. Here in Maine there are a lot of people who have camps in VERY rural areas and those camps are usually empty for long stretches of time, most often in the winter. These camps are usually easy targets for thieves. I once had a friend who had a camp in very northern Maine and it had been broken into several times and he had just gotten tired of it. He decided to take matters into his own hands. He boarded over the windows so that anyone breaking in would either stop or go through the door which he had padlocked as well as deadbolted. Just inside the door he had mounted a metal plate, with a coil spring welded to it, to the wall. Inside the the coil spring he placed a 3' length of 4x4 that he had rounded the end of so it would fit in the coil. He then mounted a catch/release mechanism that he had fashioned from a gate latch 3' away on the same wall. To this he attached a lenth of steel cable with a small piece of L-bracket welded to it. When he left for the season he simply wound the 4x4 back to the catch on the wall and ran the cable along the floor which he secured in place using a cople of electricians stapes. The cable length was adjusted so that the door would hit the pice of L-bracket/trigger when the door was opened app. 2/3 of the way or about 60 degrees. This would allow him to pen the door and slip through without setting off the trap but would set the trap off if someome busted through the door. This whole mechanism was set about 12" off the floor so that it would hit the intruder below the knees, ouch! Before he left he hung a sign on the door that said, Enter at own risk, which was there as a warning as well as a reminder to himself. He returned there that winter to find the door open, the trap sprung and a bloody trail through the snow. Apparently two people had tried to break in a day or so before and he was able to follow the trail to where they had parked the car. Later that week he was in town, a very small town by the way, and he saw a man walking on crutches with casts on both legs. He walked up to the guy and introduced himself and the other man did the same at which point my friend says, you wouldn't have any idea who broke into my camp would you, he is probably walking with a bit of a limp. His camp did not get broken into after that.