How would you handle this situation?

[Stephen Barretta]

After a long drawn out eviction of a SFH on Long Island NY, we needed to have some work done (painting, new light fixtures, patch some holes, and basic plumbing, such as a new toilet, install vanities with faucets, and new shower fixtures. We hired a plumber a few days ago and he agreed to start working last night. He requested half of the money ($750) after 1st day and rest upon completion. Around 2 hours after he left (worked until around 11:30pm) there was a major fire. House is now boarded up and condemned. Initial investigation reports that not electrical and no sign of arson. He has called many times and wants to get paid. We said we won't pay until the cause of fire is determined. How would you handle this?