guilty or not guilty

If he is forgiven for his sins then no he won't go to hell.

The key issue here is that you state he 'decided' to be a serial killer. Had you said that he 'turned out' to be a serial killer then there could be a judgmenet of diminished responsibility due to his upbringing, but as he made a clear choice to take this path he needs to be fully responsible for his actions. Religion has absolutely nothing whatsoever to do with it given the facts.

The problem, if it is a problem, with this hypothetical situation is that it can be applied to every crime or misdemeanour ever committed. Few people grow up as you describe but just as few have a perfect upbringing. Everyone's behaviour is hugely influenced by their upbringing and the smallest things in childhood can affect you for the rest of your life. For example, my mother was alaways berating me when I was small for not being ready on time. Now, I find it very difficult to be on time for anything. I saw this in action with my own son. He is a little accident-prone and my ex boyfriend kept commenting on it, joking about how clumsy he was. I noticed that my son got much much clumsier as a result and had to ask my ex to stop saying it. We are defined by the people around us. They tell us who we are and what we are like. At an age where we have less ability to question the opinions of others, this has a huge impact and being told we are always late, clumsy, evil or anything else becomes our truth. From this it could well be argued that no one is responsible for crimes they commit since they could do no other than act in accordance with the character shaped by others. There is a novel by Ouspensky called 'The Strange Life of Ivan Osokin' written to illustrate this point. The protaganist goes back to live his life again and finds that he is incapable of behaving differently the second time around even knowing the consequences of his actions. The reason Ouspensky wrote this is because he was a follower of a man called Gurdjieff who teaches that we are all 'asleep' in every day life. All our actions are entirely controlled by our circumstances and we have no free will. The only way to overcome this is to wake from our robotic state and to focus on becoming aware in every moment. That way we are fully able to choose the life we live.