As noted, you cannot condition reimbursement on the consumer's filing of a police report or because he or she failed to cooperate to your satisfaction. However, you may have at least one tool.
See 12 CFR205.11(b)(2) Written confirmation. A financial institution may require the
consumer to give written confirmation of an error within 10 business days of an oral notice. An institution that requires written confirmation shall inform the consumer of the requirement and provide the address where confirmation must be sent when the consumer gives the oral notification.
If you do require written confirmation, then you are entitled to the benefits of 205.11(c)(2)(i) which allows you to extend the investigation period to 45 days if you provisionally recredit the consumer's account:
… An institution need not provisionally credit the consumer's account if:
(A) The institution requires but does not receive written confirmation within 10 business days of an oral notice of error;
If you interpret "written confirmation" as having a form for the consumer to fill out that includes the details you need, there are alternative benefits. First, if they fill it out you have what you need and it fixes the consumer's story regarding the unauthorized transfer. (Occasionally, it seems that sometimes their stories change with each telling.) Alternatively, if they do not send the form back in a timely fashion, you are entitled to take 45 days to investigate without provisionally recrediting the account.
While you cannot condition your liability on the consumer's cooperation, his or her failure to cooperate may buy you some time.