'Parasite' Star Lee Sun-kyun Begged Police Not To Publicly Reveal Drug Probe

'Parasite' star Lee Sun-kyun had begged police not to publicly announce he was under investigation for using illegal drugs ... 4 days before his apparent suicide.

Police officials confirmed Thursday that Sun-kyun's lawyer requested cops to close the latest questioning round to the press on Saturday ... but they declined.

A day before Sun-kyun's body was found, his lawyer added the actor was hopeful any future interrogation would be in private ... explaining he felt burdened discussing the allegations in a public setting as the media coverage had been intense.

While the Incheon Metropolitan Police Chief, Kim Hui-jung, expressed deep regret over Sun-kyun's passing ... he stuck by their tough line of questioning -- adding it had been done with his consent.

As we reported, the South Korean actor was found dead, aged 48, in his car Wednesday in the capital city of Seoul ... after his manager reported him missing to the police.

He was under investigation for a drug blackmail plot ... accused of using marijuana and other substances at the home of a hostess from the local bar -- though he claimed she deceived him into taking the drugs and tried to blackmail him.

He was last questioned by police on Dec 23 ... and was detained for 19 hours before being released.

Two suspects – a man and a woman – were arrested in connection with the narcotics investigation ... and a day before Lee was found dead, he requested through his attorney that police administer a lie detector test to him and the two others.

It's not clear if they were given the polygraph exam.