Dear Mr. Rao, your presumptions are exactly correct, and the final question following your astonishment is apt. As far as I know, for any theft of the Bank's money kept in the ATM by burglary, the concerned employees of the Bank would not be proceeded against. Normally, a group of ATMs would be under the scrutiny of a monitoring system, and only the employees in charge will have access to the monitoring system to watch the entire transactions through every ATM and load them with currency as and when required.
Therefore, if a shortfall in cash between successive ATM replenishments is noticed, then normally the employees concerned would be held responsible, as they alone would have the key for the machines and know the passwords if outside agencies are not engaged for such work. Though the single key was with the cashier and the questioner, as admitted by himself, was not present at the time of the particular successive replenishment of currency, he, as the Head Cashier, cannot disown his joint responsibility for the monetary loss. Moreover, the shortfall in cash might have been detected by the Manager, and hence his suspension might be based on such presumable facts only. I gave my reply as above.
Thank you.