A court in Germany has convicted three men of stealing over four km (2.5 miles) of rail track, weighing nearly 500 tonnes, to sell as scrap metal.

The court in the city of Marburg said on Tuesday the men, aged 26 to 29, pretended to be working for the national rail operator Deutsche Bahn when they began carving up a disused line between nearby Niederwalgern and Lohra with blowtorches.

"They even went around handing out leaflets to locals asking for understanding about the noise," a court spokesman said.

"The stolen tracks were worth about 170,000 euros ($230,000) altogether, but they'd collected less than 100,000 euros by the time they were caught."

The crime has become so famous that the regional education ministry has used it as a model for a maths exam, asking pupils to calculate the weight, volume and value of the stolen steel.

The three suspects, all Germans born in the former Soviet Union, had removed 476 tonnes of steel track by the time they were caught when a local man contacted Deutsche Bahn to check their story. Two suspects confessed and received 18-month suspended sentences. The third was given two years and one month in jail.