They can be conducted in cipher, can be conducted anonymously, and they leave no trail.

[Professor Rat.]

The nature of electronic crime

Electronic transactions take place at the speed of light. They can be conducted from anywhere in the world and can be routed through multiple jurisdictions to conceal their place origin and to place obstacles in the path of investigators. They can be conducted in cipher, can be conducted anonymously, and they leave no paper trail.

It is never an easy task to investigate and prosecute commercial crime, even in a paper-based environment. Investigators and prosecutors have to build a case on the basis of what records are left when the relevant transactions have been completed. Even in a paper-based environment, the records are rarely complete, they are often misleading, and they only ever give a partial picture of what occurred.

The problems are magnified in an electronic environment. Electronic records are easier to manipulate and disguise than paper-based records. They also do not have the handwriting, signatures and other physical features that can give clues to the identity of the people behind a paper-based transaction.

If the records left by an electronic crime still exist by the time the investigators come to look for them, the investigators should be able to show what transactions took place, but it may still not be possible to identify the individuals behind those transactions. That is so even if the transactions were conducted under cover of a PIN number, password or other electronic identifier.
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http://www.austrac.gov.au/text/publications/agec/evidence.htm