What is the difference between auditing and investigation?

I agree with Ahmed Alkhamali answer. 

For me, I see that auditing is when you proof-read to make sure it is accurate and error-free and there wasn't some bad event prior to it. On the other hand, investigation is when you do more than that because there was a wrong/bad event prior to it to begin with.

So, you might say that Auditing is a daily task while investigation is evental only.

n general, Auditing is conducted to verify the extent of truthfulness and fairness of the financial records of an entity, but Investigation is performed to prove a certain fact. The scope of the auditing is based on the Standards on Auditing but the scope of investigation is based on the terms of engagement. It is quite normal, that people get confused between these two terms easily due to lack of knowledge and proper understanding.