Circumstantial Evidence is evidence that does not directly prove a conclusion, but can be linked with other evidence to deduce what happened. It requires inference and reasoning to connect the facts to the event.

In network forensics, circumstantial evidence is especially important because it is often the primary mechanism used to link electronic evidence to its creator. Unlike a physical crime, there may be no human witness. Instead, investigators use artifacts and correlations to build a chain of inference.

Key uses in digital forensics:
- Establishing the author of emails, chat logs, or documents
- Authenticating Digital Evidence, which is required for admissibility
- Linking a person to a device, account, or network activity

A notable example is United States v. Simpson, where prosecutors authenticated Internet chat logs by showing that the user "Stavron" gave the defendant's real name and home address, used an account registered to the defendant, and had records in the defendant's home matching information sent during the chat.

Examples:
- An email signature or nickname
- A file containing password hashes on a defendant's computer
- The serial number of a USB device
- Account registration details matching a suspect

Source: Network Forensics: Tracking Hackers through Cyberspace, §1.3.4.