I would guess that any relationship between bed wetting and homicidal serial offense is an illusionary correlation. I work with a psychiatric population. No one I am working with at this exact moment has killed anyone. A significant proportion of them are bed-wetters. It happens for many reasons.
Some times is it psychological.
If we were so good at predicting future behavior we would have a flawless risk assessment system in place. We are note even close to being able to make such statements. What begins as legal, victimless, symbolic behavior becomes a stepping stone to some of the most violent acts a person can carry out against others. This in the few cases where it does escalate in this manner would be true. But lets be serious here.