The Four Principles of Computer-Based Electronic Evidence
Principle 1: No action taken by law enforcement agencies or
their agents should change data held on a computer or
storage media which may subsequently be relied upon in
Principle 2: In exceptional circumstances, where a person finds
it necessary to access original data held on a computer or on
storage media, that person must be competent to do so and
be able to give evidence explaining the relevance and the
implications of their actions.
Principle 3: An audit trail or other record of all processes
applied to computer based electronic evidence should be
created and preserved. An independent third party should be
able to examine those processes and achieve the same result.
Principle 4: The person in charge of the investigation (the case
officer) has overall responsibility for ensuring that the law and
these principles are adhered to.
---From the Good Practice Guide for Computer based Electronic Evidence - ACPO