Police have reached a tentative conclusion that Koh Yu-jeong, who is suspected of murdering her ex-husband, killed her 5-year-old stepson as well.

Cheongju Sangdang Police Station said Wednesday that investigators believe Koh, 36, murdered her stepson -- her current husband’s biological son -- after a five-month probe into the case. Cheongju police booked Koh and her husband in June on suspicions of murder and involuntary manslaughter, respectively.

Based on the couple’s testimonies, profilers suspected that Koh might be involved in the death of the child, whom she appears to have seen as an obstacle in her marriage.

 
Police said a digital forensic analysis of Koh’s smartphone revealed she was awake in the hours her stepson is presumed to have died, past midnight on March 1. He was found dead by Koh’s husband, who was sleeping next to him, at around 10:10 a.m. the next day. Koh told police she had slept in another room.

Koh’s husband testified that his wife had fed his son curry the previous night. The same dish was served to Koh’s ex-husband on the day he died. Police suspect zolpidem, found among Koh’s belongings, was added to the food to facilitate the murder of the man who towered over her at 180 centimeters tall.

Police said the final results of the probe would be announced after consultation with prosecutors.

Koh is suspected of murdering her former husband and dismembering and disposing his body between May 25 and 31 at a vacation home on Jeju Island. She was arrested June 1 at the parking lot of her apartment in Cheongju, North Chungcheong Province.

Koh has admitted to murdering her ex-husband, but claimed it was an act of defense against his rape attempt.

Her fourth hearing is slated for Sept. 30 at Jeju District Court.

By Kim Arin (arin@heraldcorp.com)