It is a different model running an older operating system than the iPhone 5C belonging to Syed Rizwan Farook.
Federal authorities are weighing whether they will tell Apple about the flaw that let them access the locked phone.
The FBI says it may never reveal what investigators found on the phone.
There are at least 63 other cases where the government tried to get tech companies' help getting into devices.
Law enforcement groups backing the FBI in its fight with Apple over a locked iPhone say there is a bigger issue in the case.
The fight between Apple and the FBI over a locked iPhone gets even more personal.
Apple's top lawyer lambasted the brief as filled with "false accusations and innuendo."
The highly watched case is separate from the one focused on a phone belonging to one of the San Bernardino attackers.
The U.N. joined Facebook, Google and many other tech firms in backing Apple in the fight with the FBI.
Representatives from the FBI and Apple testified on Congress as their war of words continued.