What to do if someone took something of mine from the bank

Hi I lost something of mine in the bank and I later find out from the CCTV footage that someone who came in the bank took it with him , I also find out that the same person who took something of mine also took some kind of printed statement and the footage of that person is not that clear , And since few people take's statements in any particular day I ask to the bank branch manager of that branch to tell me the contact details of that person on the basis of the timing so that i can talk to him and recover my thing from him , the manager of that branch he told me that they can't find the person on the basis of time on the statement or in any other transaction they do in the bank and told me that they ony get the date on any transaction they do & refuse to give me any contact details of any person who took statement on that day , they didn't even told me no of people who took statement on that day , In case he was the only one that day who took statement It would have made my case easy. So please tell me what needs to be done here , how can I recover my thing from the same person who took my thing or what is the bank's responsibility regarding this.