It has been revealed through supplementary investigations by the prosecution that the police did not even check one year of mobile phone communication records for Jang Yoon-gi, the suspect in the Gwangju high school student murder case.

After receiving the case from the police, the prosecution secured and analyzed Jang's mobile phone communication records, three years of financial transaction history, and dashcam footage from vehicles near the crime scene.

As a result, the prosecution indicted Jang on charges of murder including rape, rather than simple murder.

Previously, the Gwangsan Police Station had referred the case to the Gwangju District Prosecutors Office on May 14, nine days after the incident, applying charges of simple murder against Jang.

However, after summoning Jang for questioning four times and conducting additional searches of his studio apartment and SUV, the prosecution discovered a dashcam SD card that the police had failed to secure.

The SD card was hidden inside a toolbox in the vehicle's trunk. It reportedly contained a recording of an acquaintance telling Jang, "If you had lived the way you usually talked about, you would already be a sex offender."

The police had previously searched the vehicle but failed to find the SD card and returned zip ties without seizing them.

The prosecution also analyzed one year of Jang's mobile phone records to investigate his associates, his movements before and after the crime, who he contacted, and whether there were any accomplices.

Furthermore, the prosecution analyzed three years of Jang's financial account transactions and credit card usage history to determine how frequently he purchased adult products, such as sex dolls, to uncover whether there was a sexual motive behind the crime.

It was also revealed that although the police initially discovered two sex dolls with damaged chest areas in Jang's studio apartment, they did not seize them, and Jang's father subsequently broke them into pieces and disposed of them.

The prosecution also re-analyzed the evidence already seized by the police.

When the footage from a dashcam in a truck near the crime scene, which had been secured by the police, was found to be of poor quality and difficult to identify, the prosecution initiated image enhancement work.

As a result, they confirmed footage showing the rear passenger door of the vehicle open and the suspect attempting to force the victim into the vehicle.

In effect, the supplementary investigation has uncovered specific circumstances indicating that the crime was not accidental, as Jang had claimed, but rather a murder committed after he planned and attempted sexual assault and the victim resisted.

Reported by Kim Minjeong | Video by Kim Na-on | Graphics by Yook Do-hyun | Produced by SBS Digital News