In November 1987, nine-year-old Christina was found sexually assaulted and strangled in the western city of Osnabrück.
"The girl did not hear her alarm clock, which is why she left late for school without the friends she usually walked with," said public prosecutor Alexander Retemeyer.
"She took a shortcut crossing through a garden where it was a bit dark. That is where she encountered a 19-year-old man."
The young man tried to rape her and when the girl threatened to tell her mother, he strangled her, the prosecutor said.
The victim's clothes were sealed and stored and particles of the killer's skin were removed as evidence.
"With scientific progress in the meantime, it has been possible to isolate the DNA and the case was featured on the television show Aktenzeichen XY (about unsolved crimes), which led us to tips about a suspect from a viewer," Retemeyer said.
"The suspect was ordered to provide a DNA sample, which matched what we
had. He was arrested Sunday morning and confessed Sunday afternoon."
The man, now 45, was remanded in custody on a charge of murder to cover up a crime.
"The special charge is important because the statute of limitations on a killing alone has run out," Retemeyer said.