Rudolf Richter, 74, Wilfried Ackermann, 73, and Lothar Ackermann, 64, dubbed the "grandpa gang" by German newspapers, each face up to 15 years in prison if found guilty.

Prosecutors allege the elderly trio masterminded a string of robberies at banks across western and northern Germany over a 16 year period between 1988 and 2004.

The men, who were arrested last year in a parking lot near Dortmund, had been the subject of an intense, high-profile manhunt led by "taskforce grandpa" (SOKO-Opa), a special detective unit.

The accused robbers led a fairly modest lifestyle, helping them to elude capture, a police spokesperson told the tabloid Bild: "They apparently tucked away much of the money in a retirement plan."

Armed with loaded pistols and fake hand grenades, the unusually spirited seniors allegedly forced customers and bank employees to the floor and demanded large amounts of cash.

No one was injured in the raids, although a shot was once fired — mistakenly, according to the defendants.

The two eldest members of the trio have reportedly confessed to taking part in the robberies, while Lothar Ackermann, the third and youngest accused accomplice, has so far remained tight-lipped about his possible involvement.

Wilfried Ackermann, who is not related to Lothar, said that he was afraid of dying penniless in a retirement home and planned to use his share of the takings to buy a farm.

"You really wouldn't believe how easy it is to rob a bank when you have already done it twice before," said Ackermann, who already spent 40 years in prison for previous robberies.