A con man duped a security guard of a cash collection van of Rs.15 lakh outside a mall here, police said Tuesday.A cash collection van of a private firm was parked outside the Lifestyle Mall on the Mehrauli-Gurgaon road.Gunman Yogesh was guarding the van while the other staff of the cash collecting firm were collecting money from traders inside the mall."A con man told gunman Yogesh that some cash was lying near the van. Yogesh got down from the van and started picking up the currency which was in Rs.10 notes and amounted totally to Rs.250," said a senior police officer."After some time, the gunman realised that a bag containing Rs.15,22,000 was missing from the van," he said.A case of theft was registered at the sector 29 police station.