It appears that the smart fellow understood the flaw in your process. After every credit or cash collection, there should have been reconciliation by the back end office. This was not done. Secondly, in this age of online banking, what was the need to authorise the field staff to collect the cash?
When field staff took some company property outside the company premises, how many pieces did he take and how many did pieces he return to the back office, why daily accounting was not made? When courier companies hand over the documents to the courier for delivery, in the evening everyday supervisors check how many documents he had taken and how many undelivered documents he has brought back. Supervisor check the Delivery Sheet of each courier. Did you have similar arrangement?
You can lodge the police complaint. However, you need to have evidence misappropriation of the funds. When the retail shop owners (retailers) gave some money to the field staff, did they take any receipt from him? If yes, then it can become evidence.
Above all, have you taken any agreement from the field staff about cash transaction? Couriers, or delivery staff of e-commerce companies also collect the cash from their customers. However, they are authorised to do so and undertaking is obtained from them on when the cash should be deposited, with whom it should be deposited and in return, what receipt they will get.
Anyway lessons are always learnt hard way. Rs 15,000/- is not that big amount. Hope you improve the internal processes hereafter.
12th July 2016 From India, Bangalore