SEOUL, April 14, 2025 (BSS/AFP) - The criminal trial of former South Korean president Yoon Suk Yeol opened Monday, with the impeached leader in court to defend himself against insurrection charges over his short-lived declaration of martial law.

Yoon was formally stripped of office earlier this month, after being impeached and suspended by lawmakers over his December 3 attempt to subvert civilian rule, which saw armed soldiers deployed to parliament.

He became South Korea's first sitting head of state to be arrested in January in connection to the criminal case against him, although he was later released on procedural grounds.

Yoon attended the trial at Seoul Central District Court on Monday morning and was asked by the justices to state his name, date of birth and other personal information, according to pool reports.

The presiding judge referred to Yoon as "former president" and asked, "Defendant Yoon Suk Yeol, your occupation is former president -- what is your current address?"

The court will hear witness testimonies from two military officers called by prosecutors, including one officer who claims he was instructed by top commanders "to drag out the lawmakers gathered in the National Assembly to lift the martial law".

Lawmakers defied armed soldiers and climbed over fences in order to gather in parliament and vote down Yoon's martial law declaration, forcing him to backtrack in a matter of hours.

Experts say his criminal trial is likely to be a lengthy one.

"The first verdict is likely to be delivered around August, but the case involves around 70,000 pages of evidence and numerous witnesses. So if deemed necessary by the court, the trial may be extended," lawyer Min Kyoung-sic told AFP.

Former president Park Geun-hye, for example, was impeached in December 2016 -- but it wasn't until January 2021 that the Supreme Court finalised her sentence for influence peddling and corruption.

If found guilty, Yoon would become the third South Korean president to be found guilty of insurrection -- after two military leaders in connection to a 1979 coup.

"Legal experts say that the precedent coup could be applied in the current case, as it also involved the coercive deployment of military forces," said Min.

For charges of insurrection, Yoon could be sentenced to life in prison or the maximum penalty: the death sentence.

But is it highly unlikely that sentence would be carried out. South Korea has had an unofficial moratorium on executions since 1997.