Dear Pavithra, two issues arise from your post. The first one is whether the employee in question was issued a proper letter stating that he is responsible for the protection and handover of the data that is under his custody while separating from the company. The second issue is when the employee handed over the laptop, why a check was not done to verify whether he had handed over the company property that was under his possession (in your case, soft data is company property). If the separating employee was casual and did not follow the proper procedure of handing/taking over, so was the employee who took over from him.
In fact, when the employee submitted the letter of resignation, did anyone issue instructions on the handing and taking over process? If yes, then was it through written communication? In many companies, this procedure is enumerated in the letter that conveys acceptance of the resignation. Did you do that?
There are employees who, out of malice, resort to this kind of recklessness. However, to protect the interest of the company, HR properly frames two important policies: one on the handing/taking over procedure and another on the process of separation. Without these policies or non-communication of these policies, results in the issues that you are facing now.
Thanks,
Dinesh Divekar