Tenant vacated property empty not returned keys how can I verify absence legal removal

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Tenant entered 12 month tenancy in March 2011,Paid for 5 months unpaid for 3 months.Applied to court for fast track possession section 12 notice served start contract.Day prior to bailiff repossessing applied for it to be set aside and it was as told section 8 notice had to be served despite property empty not been lived in over 2 weeks.Couple woman falsely claimed she had been assaulted by landlord.Entered the property after serving notice for gas safety inspection to find it empty with power on card meter in significant arrears.
Considering entering deposit protect scheme as current contract states deposit is penultimate rent hence no deposit has been paid 6 weeks £825 Housing advice suggested to tenant i could be fined three fold the deposit should I lodge it now or not? Tenant has changed their mobile and I cannot find them any suggestions to trace debtors?