Some US lawmakers have called the campaign to unlock the phone of the San Bernardino killer a "fool’s errand"
The FBI has acknowledged that an error in its investigation meant that it missed its window to capture data from the iPhone of San Bernardino killer Syed Farook.
James B. Comey Jr., the director of the FBI told US lawmakers that, "There was a mistake made in the 24 hours after the attack."
Apple has refused to unlock the phone - Mr Comey said that it is asking Apple to "take away the vicious guard dog and let us pick the lock," to access the shooter's data.
At times the FBI chief struggled when answering technical questions while lawmakers described attempts to force Apple to unlock the phone as a "fool’s errand."
Legislators accused the Justice Department of overreaching its authority, Apple’s general counsel said that the FBI's court order has been used as "a way to cut off the debate" around cyber security.
"This is a security versus security issue, and we believe that balance should be struck by Congress," the Apple representative said.
FBI head, Mr Comey said that he had not considered whether the enforcement of the court order would set a potentially dangerous precedent, specific reference was made to the possibility of China forcing tech companies to adhere to similar orders.