Is new landlord liable for the refund of a security deposit to the tenant?

Please see the information given below and let me know who should pay this security deposit to the tenant and what will be the new landlord role here.

1. In August, 2016, I purchased a property in Gate Tower, Al Reem Island, Abu Dhabi, where the tenant stayed.

2. His contract was until Feb 2017, so instead of returning the balance amount of rental charge, I requested the previous owner to deduct that amount.

3. After signing the contract, I received the contract between the previous owner and tenant and realized that there was a deposit AED 4,750.

4. I did not know about this deposit and transferring deposit was not even mentioned in the contract. Furthermore, the deposit agreement was between previous owner and tenant.

5. Now, the tenant wants to receive the deposit.

Please let me know whether I as a new landlord have to return this deposit or the tenant has to collect the deposit from the previous owner since they made an agreement of deposit.