As I will be carrying the cremains of both my husband and my daughter to Italy this summer, I posed the same question to tsa.
To summarize their reply: the cremains MUST be in carry-on in a container that can be x-rayed (NOT lead-lined), NO paper work needs to be carried, ubder NO circumstances is an employee ALLOWED to open the container, even if the passenger requests it.
I plan to have their ashes in small ziplocks with each name and then both bags in a larger bag.

Strange(??) so many of us got diferent answers.