I hope we can find out more about this "half-brother". Apparently, he has been living in Exile.
http://www.bbc.com/news/world-asia-38971655He was probably seen as a threat to his brother's seat of power. He may well have been a reasonable person.
Still, this would seem to show how crazy Kim Jong is, to have likely have done this; and in this manner, female assassins with needles, hypodermic, blow gun or whatever. Killing one's own "half" brother.