What you need to know about investigations faced by South Korea's former president Yoon

SEOUL (Reuters) -Since South Korea's Constitutional Court ousted President Yoon Suk Yeol on Friday, he has lost presidential immunity and is vulnerable to additional charges on top of an ongoing criminal trial concerning his martial law declaration on Dec. 3.

Yoon is currently undergoing a trial for insurrection charges, along with a former cabinet minister, several military commanders and police officials.

Here is what we know about his criminal investigations and trial so far: 

WHO IS FACING CHARGES? 

Yoon has been charged with masterminding insurrection over his martial law order. His former defence minister Kim Yong-hyun has been arrested and indicted for alleged insurrection and abuse of power. 

Chiefs of the Capital Defence Command and the Defence Counterintelligence Command have also been indicted.

Others involved in the case include former Interior Minister Lee Sang-min and army chief Park An-su, who was named martial law commander. The army's Special Warfare Command as well as several other military generals and senior police officials, including the national and Seoul police chiefs, are also accused of playing a role in the martial law plan. 

Yoon, Kim, Lee, the national and Seoul police chiefs and more than 10 military commanders have been banned from leaving the country. 

Yoon became the first sitting president to be arrested on January 15 after a dramatic showdown with law enforcement officials.

He was released from jail on March 8 after a court cancelled his arrest warrant, citing the timing of the indictment and questions about the legality of the investigation process.

WHAT CHARGES ARE SOUGHT?  

In what had been the first-ever criminal prosecution of an incumbent leader, Yoon was indicted in January on charges of leading insurrection.

Other officials also face charges of insurrection, abuse of authority and obstructing other people from exercising their rights. 

South Korean investigating authorities pursued the charge against Yoon because insurrection is one of the few criminal charges from which a sitting South Korean president does not have immunity.

However, with former president Yoon having lost immunity, he is now open to other potential charges prosecutors may bring against him.

If convicted, leading an insurrection is punishable by death or life imprisonment with or without prison labour. 

For those who engaged in activities key to the insurrection, punishment could range from death to life imprisonment down to imprisonment without prison labour for at least five years. 

South Korea last handed down a death sentence in 2016, but has not executed anyone since 1997.

People who merely joined in the plot or violence face imprisonment, with or without prison labour, for less than five years.

In February, Yoon attended in a Seoul court for his first criminal trial hearing, where his lawyers denied insurrection charges and said Yoon had no intention to paralyse the country.

The trial's first arguments are scheduled on April 14.

(Reporting by Ju-min Park, Hyonhee Shin and Joyce Lee; Editing by Alex Richardson, Ros Russell, Michael Perry and Raju Gopalakrishnan)