Look at the Korean War in two parts - pre-China and post-China.

Pre-China, the North Koreans were quite vicious. They did execute prisoners that had been captured and bound. They were fighting a war that was both fast and political. The speed meant that they weren't ready to house prisoners, so they had no other choice than to kill them. The politics of the situation was also a precursor to what would come later in North Korea - loads of propaganda.

Post-China is a different story. The Chinese were much more humane towards prisoners. They didn't execute people who surrendered, at least not as an official policy. During battles, there are records of isolated incidents of this happening, but it was low level officers, not general officers, making those decisions.

The biggest problem was simply that the Chinese were overwhelmed. They had just finished fighting a civil war, they were poor and poorly equipped, and it was winter. UN troops were also poorly equipped, many of them fighting in North Korea in October and November in summer uniforms. The majority of soldiers who died in Chinese captivity died from hunger and weather, factors that the Chinese had little to no control over given that they were trying to feed and clothe their soldiers at the same time.

For more information, any decent book on the Korean War will mention this. The two that jump out at me are Scorched Earth, Black Snow by Andrew Salmon, a book about UK/Commonwealth soldiers in the war, and The Coldest Winter by David Halberstam, about the US in the war. They don't discuss POW camps in detail, but they do mention the factors I've brought up.

Edit

/u/henry_fords_ghost said

this seems to suggest suggesting that military expediency justifies killing Prisoners of War.

I'm not saying that military expediency justifies killing prisoners of war. I am saying that North Korean soldiers did kill POWs, in part, for that reason however. As I'll mention below, the available evidence suggests that these were not systematic killings ordered by the General Staff, but the actions of front line soldiers with little training and little choice other than to let the POWs go. The South had NOT collapsed as predicted and the northern soldiers could not afford to leave people behind to guard the prisoners.

/u/GTFErinyes said:

I certainly hope you aren't suggesting that North Korea killed prisoners out of strategic need. While some cases were out of circumstances, like the notion that North Korea's most recent military experience was with/against the Japanese - who were notorious for how they treated POWs - and thus weren't as privy to Western/international regulations on the treatment of POWs, we cannot ignore that North Korea also systemically implemented a lot of policies towards POWs that were barbaric and designed to advance their own agenda.

T.R. Fehrenbach, in his book This Kind of War pointed out that there is no evidence that the North Korean leadership knew of or sanctioned the shooting of prisoners in the early part of the war. In Roy Appleman's book, South to the Naktong, North to the Yalu, he cites an order from the North Korean General Staff to all officers that said killing of POW's was strictly prohibited. The order came down on July 28th, after reports of massacres began to appear. After this order, a few more incidents occurred during the Battle of the Pusan Perimeter, but for the most part, these incidents stopped.

One Underrated fact that isnt often talked about is that the Korean POW camps would feed the prisoners about what the average citizen would eat but as Americans/most westerners were typically larger and had a higher caloric intake in their diet they would often be going hungry while eating the same amount of food a Korean or Chinese citizen would.