I think...

Wiping or erasing disk is only the first step of a complete anti-forensics attempt. The next step you would need to write some random but convincing data onto the same disk that looks like the real data before it's tampered. Any other step(s)? Be creative...

Erasing disk alone will only raise the flag and make them believe that you really hide something. Erasing disk alone is useful for cases like when a company/organization wants to sell used PCs or disks that had some (confidential) data in them.

Peace always,
<jdenny>