The report found that rebuilding five towers, as Mr. Silverstein plans to, would cost at least $7.3 billion, and that Mr. Silverstein underinsured it with only $4.6 billion, $1.7 billion of which has already been spent.

The report concluded that Mr. Silverstein will be able to build only one or two towers before being forced to default and that even if he defaults on the entire site he will net $106 million. If he holds on to the Freedom Tower and one other building he could stand to make $565 million, the report said.