Nope. Safest thing to do is delete it and pretend you never saw it. We live in a society where people are regularly punished for doing the right thing. A few months ago, I read a story where a young man was being charged with kidnapping because he escorted a lost little girl to a store's customer service department.
You may be right, but doing nothing in some cases can unravel if it ever gets turned into a witch hunt. Look at the Penn State case. After going after the coaching staff, the school started looking at Administrators and anyone in the chain of command who did not follow up on the initial events to protect the organization.
If files were to be found, the questions would be asked, "When were they discovered? How long did they exist on company equipment? Were they accessed? By whome were they accesssed?"....and so on.
From the RIAA and other lawsuits in the past few years, data custodians learned they have a responsibility to do some monitoring of the Acceptible Use Policies, within reason. I don't particularly like the way things are turning out, but while looking the other way may be an effective defense mechanism, but it can also present liabilities to those responsible.