Germany's Bild daily reported on Wednesday that, with the men's recent deaths, a chapter had closed on the 1971 abduction of Theo Albrecht, a billionaire co-founder of discount supermarket chain Aldi.
One of the ex-cons, Paul Kron, had passed away in an elderly care home in January aged 87, and his former accomplice Heinz Joachim Ollenburg had died in February at the age of 93.
Their abduction of Albrecht was one of the most spectacular crimes of its kind in post-war Germany.
They kept the millionaire hidden away for 17 days in a wardrobe in the western city of Düsseldorf, then set him free in return for seven million deutschmarks (€3.5 million).
Kron, then already a convicted burglar nicknamed Diamond Paul, was quickly caught after paying in a shop with a 500-deutschmark bill from the ransom money.
Ollenburg, his former lawyer, had fled to Mexico but was arrested there and extradited.
Both were sentenced to eight and a half years' prison, and they kept low profiles after they were released.
Albrecht, who was emotionally scarred by the kidnapping, largely withdrew from public life. He died in 2010 aged 88.
Regarding the ransom, Kron claimed Ollenburg, the brains behind the abduction, had only given him several thousand deutschmarks.
Ollenberg insisted they had split the money evenly and returned his half - leaving about 3.5 million deutschmarks missing.
Bild recounted that it had interviewed Kron several years ago.
Kron, then living on a meagre state pension, had told the daily about the missing cash: "Honestly, I don't know. I only got 10,000 deutschmarks from Ollenburg. He was cleverer than me."
Bild said it had also searched out Ollenburg, who was living near the Polish border and who refused to talk to the newspaper.
Local townspeople, said Bild, liked to gossip that "he's stashed away the money in Switzerland".