The Federal Bureau of Investigation (FBI) paid hackers to crack the San Bernardino shooter's iPhone.
The FBI contacted hackers who found at least one previously unknown software flaw in the iPhone operating system, Efe news agency quoted sources as saying on Tuesday.
The new information was used by the FBI to create a piece of hardware that allowed FBI to access the iPhone.
The method allowed them to crack the four-digit personal code without triggering a security feature used by Apple that would have deleted all the data if incorrect codes are entered more than 10 times.
It has not been revealed how much the group of professional hackers, who regularly collaborate with the US government, were paid.
The FBI finally accessed the phone of Rizwan Farook after a long legal dispute as Apple refused to provide support to FBI.
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Rizwan Farook and his wife, Tashfeen Malik, were responsible for killing 14 people in the San Bernardino shooting in the US in December.
Apple earlier said the government's demand to access the phone's data was putting user's privacy at risk.