Why did they want to make sure they got the painting? Answer: Because they knew it was valuable.
Why did they send it to Sotheby's? Answer: Because they knew it was valuable and they needed a large art-specialty auction house to validate it's worth and get the highest bid.
Seems like fraud to me. If the guy had bought the painting by himself and held it for a couple of years, I would think differently. But his inside position, coupled with assembling a group of friends, and the almost immediate re-sale through Sotheby's, pretty much seals the deal as far as I am concerned.
I would be interested in how Hale was persuaded to part with the painting. I bet there was some chicanery there, too, since the family had owned it for 100 years.