Senior North Korean military officer Hyon Yong Chol, right, attended the Moscow Conference on International Security April 16, 2015. He reportedly has been executed. Reuters

North Korea reportedly executed its defense minister, Hyon Yong Chol, as part of dictator Kim Jong Un’s latest purge, South Korean intelligence says. Hyon was one of the closest confidants of Kim, who is suspected of ordering the killings of as many as 15 high-ranking officials so far this year, according to CNN. Many reports have claimed Hyon, the military’s second in command, was killed because he disrespected Kim by falling asleep during an official meeting. But there was more to the story than a man simply nodding off.

Hyon, 66, was last seen publicly at a conference in Moscow in April, according to the Daily Express. He was reportedly arrested late last month and executed a few days later without a trial.

Hyon worked for many years under Kim’s father and predecessor, Kim Jong Il. He continued to serve as a high-ranking military officer after Jong Il died in 2011 and the son took over.

The official charge against Hyon was treason. He had apparently questioned Kim’s power in the past. The mid-meeting nap seemed to be the last straw.

It is believed that Kim’s purges are a way for the young leader to exert his authority since assuming his father’s role. North Korea has executed at least 68 senior officials under Kim’s watch. "North Korean internal politics is very volatile these days,” U.S. North Korea watcher Michael Madden told the Daily Express. “Internally, there does not seem to be any respect for Kim Jong Un within the core and middle levels of the North Korean leadership.”

Human rights groups have criticized the executions, which are often carried out by heavy artillery. "The gut-wrenching viciousness of such an act would make 'cruel and unusual punishment' sound like a gross understatement," the U.S. Committee for Human Rights in North Korea said in a statement in April, referring to reports of previous executions. "Given reports of past executions this is tragic, but unfortunately plausible in the twisted world of Kim Jong Un's North Korea."