That person pays personal bills out of the church's account. Contribution receipts aren't regularly issued to church members. When they are, members aren't encouraged to report discrepancies. A volunteer takes cash, knowing the risk of discovery is remote. Offerings aren't deposited immediately.
People dip into the cash, claiming they're using it for unauthorized expenses.
Assign more than one person to count each offering. Appoint a pool of counters. Each week two people are randomly chosen to count the offerings. Assign one person who neither counts nor deposits to reconcile offerings with bank deposits. Make at least two signatures mandatory for every check above a certain amount.