Well, since you don't actually know him, you are just speculating. I think his book is full of lies. Obviously if he is a liar, nothing he says is proof of anything.Believe it or not, Damien is a very sensitive person. As a teenager, he would have wondered about a lot of things. I think you may be placing too much emphasis on the word "feel." That was just Damien's way of talking.
Many of us might have said, "I wonder what it's like to kill someone." Because he is sensitive, Damien inserted the word that seems to be a stumbling block for you. I don't see it as blood lust at all. As Cappuccino said, without actually hearing the statement, we have no way of knowing the manner in which it was said, the circumstances under which it was said and whether or not the statement was made sarcastically.
As to Deanna Holcomb, as I have said before, she is a former girlfriend. We don't know her motive for making this statement. She may have been angry about losing Damien. She may have been being sarcastic herself. She may have been looking for her fifteen minutes. Again, without audio, oftentimes people's words can be misinterpreted.