I thought the FBI used a company in Israel to get into the iPhone(s) of the San Diego terrorists. The Feds filed a lawsuit to force Apple to turn over the unlocking procedures, but then withdrew the case when they were able to get "Cellebrite, a privately held Israeli company that specializes in transferring and extracting data from phones..." The FBI wouldn't confirm they'd used that company.
That was on an earlier model phone. The method will not work on iPhone 6 and later.
The FBI was on extremely shaky legal ground. They were not attempting to use a Warrant to get Apple to unlock the iPhone 5c, which was using an older iOS version, but an "All Writs Order" that was totally inappropriate to the case. It was essentially ordering Apple to do work that was beyond the power of the court to order. They were ordering Apple to CREATE an entirely new Operating System that would BREAK the security of iOS and then to GIVE IT TO THE FBI. This new operating system, call it FBiOS, would bypass all security. It was, by the court order, would remove all security that would protect and encrypt data, and would allow the FBI to install it on any Apple iOS. They claimed later they were only asking for THAT device. . . but that was NOT the wording of the All Writs court order.
All Writs Court Orders are usually used when you hire a locksmith to unlock a door or open a safe. It is used when you are requiring a business to do something they do in the NORMAL COURSE of their business. You cannot require them to do something they do not normally do. . . such as create a new operating system that would destroy their business model for the convenience of the court or a police agency. It also flew in the face of a FEDERAL LAW that SPECIFICALLY prohibited the courts from requiring a telecommunications manufacturer or carrier from disabling any encryption or security hardware or software for the benefit of LAW ENFORCEMENT agencies. That federal law was passed by Congress explicitly to prevent a Federal Judge from doing this. . . and the Supreme Court had already RULED a judge could NOT ORDER SUCH A THING. Apple was right to refuse to do it.