Chairman Lee Deok Man, a wealthy man of hundreds of billion dollars, was found dead in his room after being stabbed by a weapon. The entrance to the victim's room leads to the living room, while the other entrance is only a window. On either side of the victim's room are the rooms of her daughter Lee Bo Eun and her brother-in-law Kim Pil Do. The victim is usually suffering from chronic illness, so a nurse visits him regularly. Choi Mi Ran, a nurse, also visited him the same day, and Do Chang Su, the president of a subcontractor, also visited for business discussions. At the scene of the incident, President Do Chang Soo, who left his cell phone at the site, came back to take it. These are the suspects, so who is the killer? (Source: namu.wiki)