South Korea’s 2019 decision to deport without legal process two North Korean fishermen suspected of murdering their shipmates violated human rights principles, a U.N. investigator said on Wednesday, after prosecutors reopened the case.

South Korean activists had called on new President Yoon Suk-yeol to reinvestigate the case, blaming the previous government of trying to curry favour with Pyongyang amid denuclearisation negotiations and efforts at rapprochement.

While the fate of the two men is unconfirmed, there was an expectation their rights would be violated when they were turned over to North Korean authorities, and therefore Seoul had an obligation to process them in the South Korean justice system rather than immediately repatriate them, Tomas Ojea Quintana, U.N. special rapporteur on human rights in North Korea, told reporters.

“These are extremely dramatic cases because once a person is repatriated there is no reversal,” he said. “The (South Korean) government should not have repatriated these persons right away.”

Former President Moon Jae-in’s administration deported the fishermen, describing them “dangerous criminals” who killed 16 other colleagues aboard their vessel while crossing the sea border and said they would cause harm if they were accepted into South Korean society.

North Korea faces accusations of extrajudicial killings, enforced disappearances, torture, arbitrary arrests, sexual violence and forced labour. It has denied mistreating its citizens.

South Korean prosecutors have re-opened the case, Unification Minister Kwon Young-se, who handles relations with the North, told Reuters on Monday.

An official with the ministry said on Wednesday it would cooperate with the investigation.

Neither Moon, who has kept out of the public eye since leaving office, or North Korea has commented on the case.

Quintana was among several U.N. officials who sent a letter to Seoul at the time expressing concern and asking for more information. The officials also sent a letter to Pyongyang.

During this week’s visit to Seoul, Quintana also met with the family of a South Korean who went missing at sea in September 2020 while working as a fishing inspector. North Korean authorities later shot him dead and set his body on fire, shocking many South Koreans and increasing cross-border tension.

That case has also been revisited by the Yoon administration, and last week South Korea’s maritime and military authorities reversed their earlier announcements and said there were no signs the official was trying to defect.

His family had refuted the defection claims, filing a lawsuit calling for the disclosure of government records.

Quintana said he supported the family’s right to know more from the South Korean government, adding that ultimately, North Korea was responsible for killing the official, and should also disclose information, punish those who shot him, and provide reparations to the family.

North Korean leader Kim Jong Un previously made a rare apology for the killing, calling it an “unexpected and disgraceful event”, though state media said blame lay with South Korea for not controlling its borders.