I am not sure if this has been discussed in it's own thread, so I am going to create this one.
Harry has been accused of killing a mortal with magic from the very first book (his duel with Justin that ended with Justin's death).
Harry also may have killed mortals during his rage moment in Grave Peril ("Fuego, Pyrofuego") as collateral damage. It was never fully investigated therefore it was left alone, but Harry suspects he did kill at least some of the young people.
He uses necromancy to raise Sue, which while apparently is technically fine as it only applies to mortal humans for some odd reason, was still actually necromancy. The rule literally is Thou Shall Not Reach Beyond The Borders Of Life. Nothing about whether human or not. Perhaps there is a whole section interpreting this rule - the same way people manage to find exceptions in the 10 Commandments...
He also skirts the law of enthrallment when binding Toot-toot initially, as apparently it only applies to mortals. Yet still Morgan was prepared to execute him.
Finally, the only other incident I can think of is when he raises the Ghosts in Bianca's house to kill her. Now you might argue he merely attracted them and they were already around, but he actually pours magic into them to make them corporeal to a degree. Sounds like necromancy to me. Definitely only involved humans.
Can you think of any other instances where Harry uses dark magic or any other shady actions?