Andrew do you think it was because he wanted to eliminate potential claims to the throne? Really? 

I'm not sure, it seems more likely that Kim Jong Un would have his brother killed out of spite, I think Un frowns upon disrespect for authority just like his Dad, and Grandfather, I'm pretty sure that is the way they do things in The Peoples Democratic Republic of Korea... He already had his uncle killed for disrespecting him, and there were rumors recently that he (Un) had his wife killed as well, but I don't know if those rumors were ever substantiated.