Why Do They Want That?
In the case of the San Bernardino murderer, he had destroyed his personal iPhone, but the Feds wated access to his work iPhone, to see if there was any record of contacts with other terrorists. Since that phone was owned by the county, that should have been easy - except the county hadn't installed the Apple software that would have allowed them to manage all of their phones. And then the Feds changed the shooter's iCloud password, so that they couldn't even connect to the phone that way. When they finally did get in, there was nothing useful there. Big surprise, right?
In this case, there's no reason to assume that there is anything useful on his phone. There wasn't anybody else involved. And the phone wasn't owned by any government agency to give them any pretense of right.