It 'd be best if you ask a real, qualified lawyer in the country you're resigning.
In most countries though, you're under duty to return the documents to the owner ASAP, and you're eligible to some kind of compensation according to the value of the documents.
I don't think that is his main concern. In the original post he seems concerned about the legality of information learned, not so much document ownership or lost and found rights.
Even so, the details that aren't supplied in the question (which jurisdiction exactly? what kind of information was it?) are more important than the few details that are listed (where the information was found, that those are printouts).
If you want an useful answer, you need to tell more details to a relevant lawyer; currently this question can only get answers that are either useless or dangerous.
1. Are you a lawyer?
2. If so, in what jurisdiction is your qualification valid?
3. What if the taxi in question is in Zurich, say?
4. Are you going to qualify your answer in any way, or is it absolute?