The alleged agent, Ri Dong Sam, was formally detained Tuesday on suspicion of plotting to kill Hwang Jang-yop, a former senior member of the North’s ruling Worker’ Party, the prosecutor said. Police said however that there was no connection between Hwang’s recent death and the charges against the agent.

The North Korean agent came to South Korea in August by posing as a North Korean defector and was caught during an interrogation process, the prosecutor said.

South Korean intelligence officials typically question defectors for several weeks before they are sent to a resettlement center.

He has admitted some of the charges, the prosecutor said. He declined to give any further details and spoke on condition of anonymity because he was not authorized to speak to media on the continuing case.

The detention came after Hwang was found dead at his Seoul home on Oct. 10. Police said Wednesday that Hwang died from heart failure on Oct. 9, citing final autopsy results. Hwang’s body was buried at a national cemetery south of Seoul.

The 87-year-old Hwang, chief architect of North Korea’s guiding “juche” philosophy of self-reliance, was one of the country’s most powerful officials when he fled in 1997. He had tutored North Korea’s supreme leader, Kim Jong Il, on the ideology.

Hwang lived in Seoul under tight police security. He has written books and delivered speeches condemning Kim’s government as authoritarian.

North Korea had reportedly vowed revenge against Hwang, calling him “human scum” and a betrayer. Earlier this year, two North Korean army majors were each sentenced to 10 years in prison in Seoul in a separate plot to assassinate Hwang. North Korea has denied the plot.