What James is missing here is context. Kim Jong-Eun absolutely despised his older brother, partially because he was worried that he might lead a coup from exile and partially because they just didn't get along. He's been trying to kill him for years. Other than the fact that he finally succeeded, this is the least surprising thing ever.
Oldtype, I completely get that this is the message perpetuated by the South Korean state to perpetuate Kim Jong Un as a mad tyrant. Probably true but have you been to Macau? There are a lot of questions that are yet to be answered, that means the South Korean account makes no sense.
1. Why has he not been killed before? He would not have been very secure before whilst living in Macau, lots of time spent in public casinos, and his house whilst secure wasn't impenetrable.
2. If his life was permanently at risk why make frequent trips, on your own to Malaysia? He felt no threat.
3. Why has he still been working in Macau brokering deals for North Korea? How will North Korea bypass sanctions without him brokering the deals and laundering the money?
4. Why were North Korea still bankrolling his playboy lifestyle?
There's not really much of a perpetual need to perpetually perpetuate a perpetual message that Kim Jong Un is a mad tyrant. He does that just fine himself.
I have not been to Macau, but I do not see how that's relevant.
1. China has been quite clear through diplomatic channels that he is under their protection and does not want him dead. Either the Chinese don't care anymore, or KJU doesn't.
2. Precisely because his life was under threat he was known to maintain several residences across China/SE Asia and move among them at random intervals.
3. There is no evidence that he has been doing this, and it would defy all common sense.
4. He had a fair amount of assets squirrelled away before his exile, and I suspect he's received periodic subsidies from North Korean loyalists or the Chinese government.
Again, it's quite well documented that he's been fearing for his life through Korean and Japanese journalists who've had the opportunity to interview him.
It's also quite well documented that KJU wanted him dead. It's a common trope, really: the new ruler who inherited power feels threatened by the older stepbrother who has a better claim to the throne and decides to take action. The motivations here aren't difficult to understand at all.