The conclusion may pose challenges for the Trump administration in possible future litigation to force companies to help crack into encrypted devices. Senior U.S. officials have sought in recent months to revive a debate over whether encryption on devices should be weakened to allow law enforcement easier access to data belonging to criminal suspects.
Apple declined to comment.
According to a report by the Justice Department's office of inspector general, an FBI unit that breaks into mobile devices only began seeking outside help to unlock the iPhone tied to the gunman in the shooting in San Bernardino, California, on the eve of the February 2016 court filing demanding Apple's assistance.
The FBI unit chief knew that one of the vendors contacted had almost 90 percent completed a technical solution that would unlock the iPhone, the report said. The Justice Department said at the time it required Apple's assistance because it lacked other means to access the device.
Apple refused to help, prompting a high-stakes legal and public relations confrontation that ended when the FBI said an unidentified non government party had come forward with a way to crack the phone.
Communication failures at the FBI caused some officials to misunderstand the status of its own efforts to open the device, and contributed to delays in seeking help from the FBI unit and the vendor that was ultimately successful, the report said.
"The lack of coordination resulted in a "belatedly-obtained technical solution" that forced the government to withdraw its court filing stating it could not access the iPhone, it added.
The FBI told the inspector general there was no delay in developing the technique that opened the iPhone and that the vendor had proactively notified officials of the cracking method.
The review also found no evidence that then-FBI Director James Comey made inaccurate statements when he testified about the agency's iPhone unlocking efforts before Congress in February and March 2016. Comey was fired last year by President Donald Trump, who has accused him of being dishonest about private meetings the two of them had before his firing.
Technology companies and many digital security experts have said that the FBI's attempts to require that devices allow easier access a criminal suspect's cellphone would harm internet security and empower malicious hackers.
U.S. lawmakers have expressed little interest in pursuing legislation to require companies to create easier access.
FBI Director Chris Wray said in January that the bureau was unable to access data from nearly 7,800 devices in the fiscal year that ended Sept. 30 with technical tools despite possessing proper legal authority to pry them open.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)