Males killing females is not 'normal', not in the 'healthy' sense of the term, but many unhealthy behaviors are common so one might describe them as normal though they are byproducts of human intervention and so not natural. Most cases of extreme aggression, regardless of gender or age of the victim or attacker, are not 'normal' but are directly or indirectly caused by our breeding, feeding, and housing arrangements sustained over thousands of generations.
She may have been faulty, which normally would have been my first expectation, but experience with domesticated or long-term-captive animals teaches me that in most cases it's because the killer is faulty, not the victim. If he was wild, or very close to it, and I don't mean non-tamed but domestic for thousands of generations, but actually wild, then I'd think there was some fault with her. If he's from totally captive born stock he may just be one of those excessively aggressive ones, they're common enough. So, technically, it could be 'normal' but so is cannibalism and many other neurotic or antisocial behaviors.
In other animals I'd recommend killing or otherwise culling out the male, but if you're anti-hybrid I assume you have put in significant time and investment into securing good bloodlines with a view to preserving the species. (Feel free to correct me if I'm wrong). So you may want to just keep him with the female he accepts and make a note to possibly keep a closer eye on his male offspring for aggression towards their mates, so if you see it in his sons you do not put the hens back in with them after the initial attack, and preferably separate her before it escalates if ever you see the warning signs again.
It's a little surprising you put the hen back in with him after the first attack; that level of violence was severe enough to indicate the hen should never be put back in with him. Harassing aggressively, being violent, are not natural signs of sexual attraction, and should be considered warning signs, not something that will resolve itself.
In some breeds of some species we have managed to combine sexual instinct with aggression, so brutality to breeding partners is not uncommon, but that doesn't mean it's a good idea to breed on with. Plenty of roosters attack hens as they mate with them, and when they're not mating too, it's just how some are these days.
If he doesn't harm the first hen, maybe it was a one-off, maybe there was some fault in the hen like a seriously bad genetic issue or disease that he could detect, and maybe it won't happen again. Here's hoping anyway. Rare bloodlines are too rare to waste on antisocial/destructive individuals who kill instead of mate, lol.
If he can't function normally maybe he can be used for AI? He might pass on his aggression, if it is inherited, though.
I recall one issue in recent years with a rare species, of which there were only 20 individuals left, wherein an adult male was seeking out and killing adult females as well as juveniles, and for some reason they allowed this terminal behavior to continue instead of killing or capturing him. Does not make sense, lol. How precious does one individual have to be, genetically, to be allowed to destroy a large percentage of their species' last survivors?
Best wishes.
