SEOUL--The United Nations Human Rights office in South Korea called on Tuesday for an impartial investigation into the killing of a fisheries official by North Korean troops at sea last month, as the man’s family urged the U.N. to conduct its own probe.

The death of the official, whose family identified him as Lee Dae-jun, sparked a dispute over why and how he was found floating in North Korean waters nearly 36 hours after he went missing.

The South Korean government said their investigation suggests Lee wanted to defect to the North, but his family disputes that.

Lee’s brother, Lee Rae-jin, told reporters outside the Seoul office of the U.N. High Commissioner for Human Rights that he wanted to expose North Korea’s “atrocities” and ask for a “fair and objective investigation” by the U.N.

In a statement on Twitter, the U.N. human rights office in Seoul said both Koreas are obligated to carry out a “prompt, impartial, and effective investigation” and to make the findings public but made no mention of the U.N. playing a role.

North Korea should also engage with the South to return the man’s remains, the U.N. office said.

Lee Dae-jun’s teenage son wrote a letter to South Korean President Moon Jae-in accusing the government of failing to save his father’s life.

“Would you have acted the same way if it were your own child or grandchild going through this pain?” he wrote to Moon.

Moon’s office said that the president planned to respond to the boy personally.

A spokesman for South Korea’s ministry of defense said it would respond to the family after reviewing their request for information.

South Korea has accused the North of dousing Lee’s body in fuel and setting it on fire in an effort to prevent any possible coronavirus infections. North Korean leader Kim Jong Un offered an apology for the killing, but Pyongyang denied it burned his body and has not responded to Seoul’s call for a joint probe.

Ha Tae-keung, an opposition party lawmaker on parliament’s intelligence committee, told reporters that the government would also ask the U.N. to investigate whether North Korea is executing people who don’t follow anti-coronavirus measures.

North Korea has not confirmed any coronavirus infections and has imposed strict virus-control measures including closing its borders, although South Korea and the United States doubt it has managed to avoid the pandemic completely.