Four arrested accused have been remanded in police custody till March 17. Pic/Sayyed Sameer Abedi

Agencies probing the money-laundering scam involving Nirav Modi's company and Punjab National Bank (PNB) officials have found that the scam went undetected for over 10 years because the accused used the rolling-over method — PNB officials kept issuing new letters of undertaking (LOUs) to settle old ones, amounts of which ran into several thousand crores.