A weekend rapist who eliminated witnesses by strangling his victims , Peter Goebbels took to violent sex as a diversion from the daily grind of working in a factory. At twenty-three, he never let his pleasures interfere with earning money, but the ease with which he claimed his victims fostered over-confidence, and he grew careless in the end. On Saturday, July 6, 1985, a teenage boy observed a man and woman grappling in an alley, in the Lichterfelde neighborhood of West Berlin. A lover's quarrel, perhaps. He thought no more about it at the time, until pedestrians discovered the body of Marion Bormann, 17, raped and strangled near the scene of the remembered altercation. Frightened now, the boy approached police and offered them a fair description of the suspect. Meanwhile, homicide detectives had been paging through their files, compiling records of attacks that seemed to fit the killer's profile. Three more cases from the Lichterfelde district caught their eye. On Sunday night, the twenty-sixth of August, 1984, Helga Kousdoerfer, age 22, had been strangled and raped in the area. Seven months later, on March 24 -- another Sunday -- 19-year-old Liselotte Mohn had suffered an identical fate. On Saturday, June 1, the victim was Karola Eisenstein, age 20, raped and strangled like the others. In their search for likely suspects, the authorities examined one more case. A 20-year-old woman from the Lichterfelde neighborhood had been attacked in mid-July of 1984, her rapist startled into flight at the appearance of pedestrians. The suspect, Peter Goebbels, 23, had dropped his identification card at the scene, making conviction a virtual certainty, but there were problems with the case. That rape had taken place on Wednesday, and detectives in the string of homicides were searching for a killer who invariably struck on weekends. Simple homework finally revealed the link. While suspect Goebbels worked a normal five-day week on the assembly line, his plant had been closed down the retooling of machinery one Wednesday in July of 1984. Convicted of the rape, he drew a year's suspended sentence from the court, but homicide investigators kept the pressure on, including Goebbels in a lineup where the teenage witness in the Bormann case selected Peter as the girl's assailant. Goebbels broke down and confessed , denying all involvement in the other crimes while claiming he was "sick," in need of "help." A term of life in prison was prescribed as treatment for his "illness," while Berlin authorities continue seeking evidence to link him with three other identical homicides.