Regarding the question WHY it was asked by external parties to the FBI about questioning and ensuring that an iPhone had NOT been cracked by anyone within the FBI itself, I can assure you that was a request by the NSA or DIA whichever intel agency OTHER than the FBI to SQUASH any publicity about such an ability. The FBI leaks like a sieve to foreign agencies such as the GRU/SVR/CHINA, etc and ANYONE who such ability would be a ripe target for a honeytrap or rubber hose side-channel attack to get that ability for themselves!
This means ALREADY that the NSA/DIA/CIA have just such an ability to break ANY iPhone encryption and unlocking and wante dto ensure NO ONE ELSE but themselves have that capability. So they used other agencies to enquire IF otehrs had that capability!
So Here is how to break iPhone locking!
1) Burn custom version of ARM processor with register re-direction so that all values and instructions put into local CPU registers and instruction queues get exported out to an accessible memory location!
2) desolder original phone chip!
3) resolder new arm chip into socket.
4a) Copy all data registers and instruction in the CPU instruction pipeline, the keyboard PIC chip, to an external memory location for slurping by custom software.
4b) Read and Modify all registers and cpu instructions used to unlock phone and put in a
bypass (JMP code) to bypass any found the phone lock or data destruction routines.
(you may need to brick a few phones to get such information!)
5) Simply put in keycode after keycode until OS is unlocked since the password entry and data destroy or OS lock commands will ALWAYS be bypassed by the new ARM chip instructions which use a JMP command to bypass such routines.
NOW! See how simple that is....I do it myself --- works great!
Trust me on this! I can tell you the NSA especially has already burned EACH VERSION of the Apple Axx series chips (and x86, AMD, Qualcomm, TI cpus etc) and inserted a NEW instruction set and CPU register copy, re-direct and modify pipeline so they can simply desolder the old chip and put in a new one bypassing ANY phone, tablet or desktop security.
To get the CPU die schematics, all they need to do is SHAVE EACH APPLE A-series CPU CHIP LAYER BY LAYER and scan the line traces layer by layer into a microcircuit layout program and insert a new instruction set and make a few yourself more CPU's on another wafer. The new CPU doesn't even have to be the same size or manufacturing process cuz you can just put in a direct patch of wires into the socket.
That's what we did in the old days of Spook-Space on 286/386/468/Pentium/SPARC/MIPS days !!!! (i.e. 1980's/1990's/2000's) so I would expect that low level CPU modification work would continue!