What i managed to find is this.

Прилагательное имеет смысловую связь с древнерусским словом «голова», которое употреблялось и в значении «убитый».

So there was the Old Russian word «голова» which meant both 'head' as in contemporary Russian, but also had the other meaning 'killed'. My hypothesis is that 'уголовный' is derived from this word 'голова' implying its 2nd meaning, and this is the crime involving killing or murder. Later the world 'уголовный' evolved and covered more meanings including rape, assault, terrorism and other most serious crimes. And so in contemporary Russian what we have is 'уголовный' meaning all serious crimes, thus уголовно-наказуемый, Уголовный кодекс (УК), уголовник (slang word for felons).