This is a pretty long and complicated paper, but it really gets down to the intricate parts of hard drives, secure deletion of content from the drives and how data could possibly be recovered (by your hopefully hypothetical forensics officer ).

Secure Deletion of Data from Magnetic and Solid-State Memory

Very long and very detailed, but afaik if you truly want to know how secure your deletion methods are, this is the best resource.

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just saw this thread on secure data removal - it may be able to help you out.
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