Can I refuse to answer questions that may get my office manager fired?

My job is to mail out the acct-receivable statements. I have found that the office manager has been moving money from one account to another. Example, your 90 days past due on an account. She will take part of the balance and move it to a customer that truely has a zero balance. So our books show no over 90 days. And, I told someone this who in turn reported my office manager. Now I am going to be questioned about this matter by the CFO of the company. Do I have to answer these questions or produce any of the messed up stuff I have seen. I really dont want to be a part of this matter. If this is truely something that should not be happening( the creative accounting then shouldn't the Cfo have been the one who discovered this anyway?