They've probably spent six to seven figures on hiring a 3rd party for a bespoke service just to find what any analyst could've assumed - nothing.
That said given the severity of the situation even a 1 in a 1000 chance to get some additional information would'be been worth the kings ransom they must have had to pay to get it unlocked. At the end think what you want of the FBI but that's exactly what their duty should entail, forcing Apple to unlock it is a murky business but investing resources in unlock the phone themselves is perfectly within their right and even obligation to do.
I don't understand why people are going apeshit about this no one would bat an eye when the FBI picks a lock or breaks into a safe how is an iPhone different?