White collar crime cases tend to focus on the flow of money. Government investigators analyze the finances of a company or individual to determine where money came from and where it went. It is this trail of money that leads to evidence of a crime.
Sometimes the financial evidence is direct, but often it is indirect. Consider a case of alleged tax fraud, in which the government is trying to prove that a person or business had unreported income. The evidence may be large unexplained deposits to a bank account. If the source of the funds is unknown, the government may consider the deposits indirect evidence of unreported taxable income. Making such assumptions is often necessary when investigating financial frauds, as those committing fraud deliberately try to hide the true sources and uses of funds.