You can take umbrage all you like but unless you can prove that someone committing a crime has caused a large scale genetic change you're going to have a hard time proving that he's no longer human. 
Honestly, no, I don't think I would. But then, as I said more or less, I don't see it the way you seem to believe I do. The criminal can be or seem quite human. I accepted that long before I came to this conclusion. The victim is my concern.
Having met, in person, a victim of long-term abuse (this girl was pretty much trained into being a piece of furniture, and I am not making this **** up), and seen that
they have more or less lost their humanity, it is not difficult to believe a person can be reduced to less than human status. Somebody who manages to fall straight into the uncanny valley makes proving the point remarkably easy. This is not quite tangential, because it proves the other point; you
can demonstrate that someone lacks the basic instincts or morality associated with being human. And as the saying goes, it takes two to tango. An abused needs an abuser; sociopathy is a diagnosisable illness.
To revoke willfully and knowingly someone else's own humanity, in a premediated fashion, for no seriously defensible reason, is an easy route to be being diagnosed a sociopath. Sociopathy is more or less defined as lacking something intrinsically associated with human beings. It's not that hard a concept. Of course, you wish to argue biology rather than pyschology.
As I said to Trashman earlier there is a big difference between locking someone up to prevent them being a danger or even killing them in revenge for their crime and killing them because you have relegated them to whatever category (animal/monster/sub-human) you see fit in order to justify the taking of their life. That's just a big exercise in sticking your head in the sand about the whole subject. Instead of being willing to accept that humans can do really horrible things you want to relegate anyone who does something like that to sub-human.
On the contrary. Sticking my head in the sand is what I did before this.
You've instituted a false dichotomy. If I believe one crime is the result of being subhuman, I believe all of them are =/= reality. I am perfectly willing to accept humans can do horrible things to each other. We murder without premeditation all the time. This is deplorable, but it doesn't prove much about the person doing it besides that they have a temper. We go to war with each other. We steal and litter and jaywalk and start fires that end up burning down half of LA. None of these intrinsically proves very much about the criminal. It takes something serious on a face-to-face first-name basis before one instinctively reaches for the less pleasant explanations.
So yes it is a claim that they aren't human. And one I completely reject. They are human. If you want to argue that they are humans who aren't worth keeping alive that's another matter but don't expect me to blithely accept your belief that criminals who commit certain crimes aren't human. You'll definitely have to prove that before it's anything more than an assertion.
Biology vs. pyschology again. But more than that, I don't really expect you to accept it, because I know you better than that. I do expect you to make a better attempt to understand it then you seem willing to. In a way I feel insulted; you treat my argument as if it was made by some of considerably less sophistication, and I think you should know better by now. This is not the first time this discussion has been had. Did you really think I was immune to the logic of the other twenty times?