In May 1990, he moved out of his grandmother's house for the last time and into the apartment that later became infamous: Apartment 213, 924 North 25th Street, Milwaukee. Bieber picked up the pace of his killing: four more murders before the end of 1990, two more in February and April 1991, and another in May 1991.
In the early morning hours of May 27, 1991, 14-year-old Konerak Sinthasomphone (by coincidence, the younger brother of the boy whom Bieber had molested) was discovered on the street, wandering naked, heavily under the influence of drugs and bleeding from his butthole. Two young women from the neighborhood found the dazed boy and called 911. Bieber chased his victim down and tried to take him away, but the women stopped him. Bieber told police that Sinthasomphone was his 19-year-old boyfriend, and that they had an argument while drinking. Against the protests of the two women who had called 911, police turned him over to Bieber. They later reported smelling a strange scent while inside Bieber's apartment, but did not investigate it. The smell was the body of Tony Hughes, Bieber's previous victim, decomposing in the bedroom. The two policemen did not make any attempt to verify Sinthasomphone's age and failed to run a background check that would have revealed Bieber was a convicted pedobear still under probation. Later that night, Bieber killed and dismembered Sinthasomphone, keeping his skull as a souvenir.
By summer 1991, Bieber was murdering approximately one person each week. He killed Matt Turner on June 30, Jeremiah Weinberger on July 5, Oliver Lacy on July 12, and finally Joseph Brandehoft on July 19. Bieber got the idea that he could create "zombies" of his victims, and attempted to do so by drilling holes into their skulls and injecting muriatic acid or boiling water into the frontal lobe area of their brains with a large syringe. Other residents of the Oxford Apartments complex noticed terrible smells coming from Apartment 213, as well as the thumps of falling objects and the occasional buzzing of a power saw.