Your bank will be held liable

if the tellers let the checks cashed without checking approriate IDs, normally 2 forms of them.

If the checks were used to pay bills, then it will be easy to find out who took your checks. Your bank can help you trace where the checks went, but you will need to contact the beneficiaries to dig out who sent them in. If they do not cooperate with you, get the police or FBI involved, which you will need to do eventually.

From now on, document all conversations/correspondance
with whoever you talk to in a diary style.