Lee Kyung-woo, center, answers reporters' questions at the Suseo Police Station in Gangnam-gu, Seoul, on April 9 before he is sent over to the prosecution. Lee is a suspect in the kidnapping and murder case of a woman in her 40s in March. (Yonhap)

A kidnapping murder case in Seoul's Gangnam district in March that sent shockwaves through the nation took a twist on Monday when it was revealed that one of the main suspects had claimed to be a special operative trained for missions in North Korea.

Seven people including 36-year-old Lee Kyung-woo -- who is accused of masterminding the crime -- are on trial for conspiring to abduct and murder the victim in her 40s. During a hearing at the Seoul Central District Court on Monday, a prosecutor asked a witness if he knew that Lee had been a special operative.

The witness, who was also on trial for his role of following the victim prior to the abduction, said he had heard that Lee was a former agent.

An official at the Suseo Police Station who investigated the case confirmed to The Korea Herald that Lee had claimed to have an "HID agent" background, but such claims could not be verified, the official added.

HID, or Headquarters for Intelligence Detachment, is a South Korean military unit believed to have been involved in secret missions in the North in the past. The South has officially ceased infiltration missions since the signing of a nonaggression pact in the 1970s.

On the night of March 29 in Gangnam’s Yeoksam-dong, Lee allegedly had two others named Hwang Dae-han and Yeon Ji-ho abduct the victim and kill her the next morning, then bury her in the hills near Daecheong Dam in Daejeon. The trio were detained and indicted in late June.

Lee is suspected of receiving 70 million won ($54,700) from a couple named Yoo Sang-won and Hwang Eun-hee, who were in conflict with the victim after losing money in a cryptocurrency investment. The couple are also on trial while in custody.

Lee planned the crime with his college friend Hwang Dae-han and Yeon, an employee of the delivery agency that Hwang ran.

The trio allegedly injected the victim with fentanyl, a highly potent synthetic opioid known as the “zombie drug” in South Korea, which Lee’s wife surnamed Huh, a nursing assistant, took from the hospital she works at.

An autopsy revealed that the victim was strangled to death.

Lee Kyung-woo stated in the first trial on June 9 that he had no intention of killing the victim. Hwang Dae-han's attorney also claimed that Hwang hadn't intended to kill her. Yeon, on the other hand, admitted to all the criminal charges including robbery and homicide.

The couple who allegedly paid the trio denied the charges made against them.