The US government believes it may have found an alternative way of unlocking an iPhone 5C owned by San Bernardino gunman Syed Farook.
The FBI has requested a delay to a hearing that could force Apple to create a feature that would allow it to unlock the iPhone, so it can attempt to hack the device using its own method.
Apple last month rejected the FBI's suggestions that it should create a way to circumvent the iPhone's security features, and the two organisations have been locked in a fierce court battle since.
The software currently employed by Apple only allows an individual to download data from an iPhone if he or she knows the user's passcode -- which the FBI does not.
But now the FBI has performed a U-turn on suggestions that Apple's cooperation would be the only way to access the personal information stored on Farook's device -- a view it has held since Apple made it clear it would not create a new version of its operating system.
National Security Agency whistle-blower Edward Snowden had weeks ago said Apple did not need to compromise security in order for the FBI to hack the iPhone -- and his view was backed up by a number of cryptographers and data security experts.
The FBI said an "outside party" had shown it the alternative method of unlocking Farook's iPhone, and Justice Department spokesperson Melanie Newman says the FBI is now "cautiously optimistic" that it will be able to unlock the iPhone before April 5.
"If this solution works, it will allow us to search the phone and continue our investigation into the terrorist attack that killed 14 people and wounded 22 people," Ms Newman said.