It's not that surprising that it's an earthling that though of this magic.
The guy only needs to be a scientist or at least someone who like experiments and lost something like his daughter/dog or such. And the first he'll think is to create is a reviving spell. About ethics, well, it's pretty easy, he will commence with small animals. To increase gradually from bigger and bigger, and will start experimenting on humans with the excuse of "I will revive them when I succeed!".
And then you have a failed Revive Spell~