In one city, Wonsan, authorities forced up to 10,000 innocent people, including children, to watch the killings at a local stadium.
I'm still trying to understand the reasons for these terrible actions. In my eyes - and surely those of many other people - having a religion, or watching a South Korean TV drama, is definitely not a serious crime.
These victims should never have been treated so severely for doing something most of us enjoy doing.
It is even harder to understand why North Korean citizens, especially young children, are forced to watch such killings. Why do the North Korean authorities threaten and traumatise their own people like this?
It's made me think about the great freedoms we enjoy in Hong Kong. We can voice our opinions about the government and pick our own religion.
We often complain that our parents control our lives - that they stop us seeing friends, or using the internet.
Yet I realise that, compared to North Koreans, we're lucky to enjoy such liberty here in Hong Kong.