In order to be able to successfully prosecute an intruder: 

Answer options:

A. A point of contact should be designated to be responsible for communicating with law enforcement and other external agencies.
B. A proper chain of custody of evidence has to be preserved.
C. Collection of evidence has to be done following predefined procedures.
D. Whenever possible, analyze a replica of the compromised resource, not the original, thereby avoiding inadvertently tamping with evidence.

B

If you intend on prosecuting an intruder, evidence has to be collected in a lawful manner and, most importantly, protected through a secure chain-of-custody procedure that tracks who has been involved in handling the evidence and where it has been stored. All other choices are all important points, but not the best answer, since no prosecution is possible without a proper, provable chain of custody of evidence. Source: ALLEN, Julia H., The CERT Guide to System and Network Security Practices, Addison-Wesley, 2001, Chapter 7: Responding to Intrusions (pages 282- 285).