The Supreme Court Thursday upheld the acquittal of a student activist who was jailed by the former military-backed government for abetting a fellow activist’s suicide.

The highest court confirmed the ruling by lower courts that delivered a not-guilty verdict to Kang Ki-hoon, citing the “lack of credibility” of forensic evidence.

Kang, 51, was convicted in 1991 for helping a fellow activist Kim Ki-sul set himself on fire and jump to his death from a university building in Seoul, and ghostwriting Kim’s will in protest against the authoritarian administration of the then-president Roh Tae-woo.

Though Kang denied the charges, he was sentenced to three years in jail after the National Forensic Service confirmed that he had written the suicide note.

The 1991 ruling came when a rash of protests engulfed the nation, demanding more democracy and the resignation of Roh.

In the case that later became known as Korean version of the “Dreyfus Affair,” it is widely thought that the authoritarian government framed Kang to sway the public opinion against the sprawling protest movement.

Kang sought a retrial in 2008, a year after the Truth and Reconciliation Commission, a special committee established in 2005 to review past security-related cases, concluded that Kang did not write the note and prosecutors framed him.

Strong opposition from the prosecution delayed the retrial for years, but the Seoul High Court finally acquitted Kang in February 2014, which was upheld by the Supreme Court on Thursday.

The Seoul High Court, however, convicted him of violating the National Security Law, sentencing him to one year in jail and partially depriving him of civil rights including his right to vote for a year.

As Kang has already served a jail term, he will not be put behind bars, the court said.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)