If you've got nothing to loose relationship wise with your neighbor... take him to court. At least he will have the opportunity to explain himself to you and the judge when you question him or plead the 5th...
If he hired a laborer and not a contractor, he as the employer would be responsible... that is why I only hire licensed and insured individuals...
My Neighbor refused to turn over the info on his tree trimmer... I went ahead and had the damaged repaired and neighbor offered to pay for the parts... I did the work myself. Never did find out who the guy up in the tree was.
I'm certain the trimmer was illegal... frustrating as all get out...