An Unsolved Murder

My father works at the police department, and that's where he learned about this story. It was 2008. The police received a call from a man who said his neighbor hadn't left her apartment for a week. He said there was a terrible odor coming from the apartment. Two officers responded to the call. As soon as they got to the sixth floor, where the apartment was, they, too, smelled the stench. They rang the doorbell several times, knocked, and asked for the door to be opened, but no one answered. Then they decided to break into the apartment. OMON (special forces unit) and an investigator arrived. They forced the door open. The stench brought tears to everyone's eyes. They found the decomposed body of the woman in the apartment, tied to a chair—someone had tied her up and stabbed her with a knife at least two weeks earlier. Occult symbols, written in the victim's blood, were scrawled all over the walls of the room. The deceased woman was about 30 years old.  The cause of death wasn't determined, but there was one alarming detail. The front door, the windows, the balcony exit—everything was locked from the inside. Investigators thoroughly examined the apartment, took fingerprints, and discovered that after the murder, no one could have left the apartment without leaving traces of their presence—it seemed as if the killer, having done their job, simply vanished... So the case remained unsolved.