Police in Rome have discovered a new system used by thieves to steal money by tampering with bank machines.

Known as "cash trapping" the method involves inserting a metal clip into the banknote dispenser, in a manner invisible to the naked eye. The procedure of withdrawing money functions as normal until the appearance of the words "operation complete/amount paid". After that however, the notes are not forthcoming. At this point the customer usually blames the malfunction on a technical failure, and leaves the scene, allowing the observing thieves to retrieve the metal device and with it all the banknotes trapped inside.

Police from Rome's Porta Portese station happened upon three Romanians acting suspiciously at an ATM on Via Francesco Grimaldi in the Portuense district. After the police intervened they found that the bank machine contained some €1,400 of trapped notes that the thieves were attempting to free. Further investigations led police to another ATM on Via Stefano Jacini, near Corso di Francia, which had also been tampered with in a similar fashion. The three thieves were arrested on charges of aggravated theft.

Police have advised that if users of bank machines in Rome do not receive their requested notes when the bank machine says it has paid the money, they should not leave the ATM but call the emergency police number 112 instead.

While older forms of bank machine theft such as "skimming" and card trapping have generally decreased across Europe, incidents of cash trapping have increased from 240 cases in 2010 to over 10,000 incidents in 2011.