The now 64-year-old man was identified by a saliva sample he had given detectives during their 1984 investigation of the murder of Gabriele Stender.
More than 150 men in the Segeberg area near Kiel, volunteered last year to give samples to help the hunt for her killer as police wanted to use modern DNA identification techniques to make a last attempt to find the man responsible.
Little did the detectives realise when they arrested the family man who had lived a quiet life for decades that they were dealing with a serial killer.
He admitted killing 18-year-old Gabriele Stender, saying he had picked her up as she hitch-hiked to a disco, then raped and strangled her with her own scarf.
Then he told detectives he had also killed four other young women in northern Germany between 1969 and 1972. They said on Friday they had no doubt he was telling the truth about the two 16-year-olds and the two 22-year-olds he said he had also killed.
They said his attacks always followed the same pattern - he would watch a young woman from his car, follow and then suddenly attack her, before killing her. Further details will not be released to protect the investigation.