Ekumbaba Ltd is a small wholesaler of model aeroplanes. It only has a few employees. The owner of the business, who is also the manager, makes daily deposits of customers' cheques into the firm's bank account and writes all cheques issued by the firm. He also reconciles the monthly statement with the books when the bank statement is received in the mail.

The assistant to the owner renders secretarial services, which include taking dictation, typing letters and processing all mail - both incoming and outgoing. Each day, the assistant gives the owner the cheques received from customers. The vouchers attached to the cheques are separated by the assistant and sent to the bookkeeper, along with any other remittance advices that have been enclosed with the cheques.

The bookkeeper makes prompt entries to credit customers' accounts for their remittance. From these accounts, the bookkeeper prepares monthly statements for mailing to customers. Other employees include marketing and warehouse personnel.

It is possible that the owner's assistant takes customers' cheques (depositing them in his or her own account) and destroys the remittance advices and vouchers accompanying these cheques.

How would such a theft be concealed? What precautions could prevent the theft and/or its concealment?