Addressing the Query on Negligence and Handover Procedures
First and foremost, the section where you have posted your query is incorrect. You should have posted it in the "Human Resource Management" or "Talk to Seniors" section.
Coming to your query, would you mind elucidating further on the "negligence"? Secondly, if a warning letter is issued, it should have the support of some SOP, policy, rule, and regulation, etc. Do you have a formal policy on "Employee Handing/Taking Over"? If not, then why is it not in place?
If the employee was proceeding on leave, then who approved his leave? Was it not the responsibility of the senior to ensure that his/her junior is properly relieved and confirmed well in advance to whom that employee should hand over?
If the employee left on leave due to an emergent situation, then why was a standby arrangement not in place? In emergency cases, I have seen people handing over and taking over properly before leaving.
From my point of view, the senior of that employee is more responsible. You should issue a warning letter to him for allowing the junior to go on "Annual Leave" without a formal handover. What is supervision otherwise? This is what supervision entails. On the day the employee went on leave, on his last day, the superior should have asked for a handover and taking over register duly signed by both employees.
Though I am not clear on the facts of the case, I do not appreciate making the junior a scapegoat if proper instructions were not given to him.
However, if you have the policy on handover and taking over in place, and the employee who went on leave knew it well, and the authority who approved his leave had instructed him on whom to hand over the charge, then the situation merits more than just a warning letter. Upon his return from leave, give him a show-cause notice and ask for an explanation. If the explanation is not found satisfactory, give him the appropriate punishment.
Thanks,
Regards,
Dinesh V Divekar