I spanked my son, after I think about 2 years old when he could understand it and was being extremely defiant, when words were not enough to control him.
As a mother I do feel like I had to spank my boy.. to keep him under control, to show him that momma doesn't mess around! He is a very very respectful child, I was get a lot of compliments on his behaviour, everyone is so impressed how mature he acts for his age, he is brilliant in school, lives an amazing social life, he is all around a great child!!
He is 5, and I barely have to give him a spank now, I can just lift my hand and he will already know I mean business- and this is good. This shows him not to push me.. or there will be consequences. When my father spanked me as a kid.. I told myself 'id never do this to my kids' yet ... I have and its only when every other discipline measure is not working!
A is still young so I haven't had to spank her yet.. I mean the usual age for them to need a spank is around 2. I think under 1 years old in unnecessary as they have no idea what you are doing, and you are teaching them to hit.
Anyways I dont think. criminals, and murders have anything to do with spanking, its the general upbringing and personality traits.