The reports in South Korea's Chosun Ilbo newspaper indicate that Hyon, a singer with the Unhasu Orchestra, was among those arrested on August 17 for violating domestic laws on pornography.All of the victims were in the same band, the Unhasu Orchestra or the Wanghaesan Light Music Band, and regularly performed for Kim Jong-Un. You can see a 2011 performance here:
All 12 were machine-gunned three days later, with other members of North Korea's most famous pop groups and their immediate families forced to watch. The onlookers were then sent to prison camps, victims of the regime's assumption of guilt by association, the reports stated.
Many are skeptical about the motivation behind the executions:
His father, Kim Jong-il, did not approve of the relationship and ordered him to break it off. Hyon subsequently married an officer in the North Korean military and reportedly had a baby, although there are suggestions that Hyon continued to see Kim after her marriage.
Kim's wife, Ri Sol-ju, was also a member of the Unhasu Orchestra before marriage and one theory is that Ri objected to the continuing high profile of her husband's former girlfriend.