If the boy does not kill /another person/, then I would say that 'ucide' is better.
My understanding is that 'a omorî' refers to killing things in general; e.g. people, animals, plants, bacteria - and that 'a ucide' is used more specifically for the crime of murder.
Very stupid sentence, however, guess what, Romanian has synonymous, just like English, even more actually. Ucide is synonymous with omoară. But as always, the editors take a piss about our feedback.