What are you doing to prevent future repeats of whatever has happened to your pond?
Which brings the question - did / do you not have surveillance on your property? If you didn't for the period in question, or you don't have the footage for the period in question, perhaps consider installing equipment pretty quick.
From what you've described, you most likely will want a near real time solution that sends the data to your mobile device as soon as the file is written. In case you happen to be home when the next event occurs and you can head them off at the pass if you will. Before they dump their fish into your pond from their bucket.
You might also consider posting signs indicating your private pond is not for use and research is being conducted so please do not introduce any fish, amphibians, or mammals to your pond. Sometimes signs work.
