Rumors have suggested the FBI employed Israeli mobile forensics firm Cellebrite to hack into the iPhone 5c used by San Bernardino shooter Syed Farook, but new information from The Washington Post suggests it was instead done with the help of "professional hackers" at least one of which is a "gray hat" researcher that sells flaws to governments, black market groups, or companies that create surveillance tools.

According to sources who spoke to The Washington Post, the hackers told the FBI about a previously unknown software flaw, which was used to "create a piece of hardware" the FBI used to access the phone via its passcode. The hardware in question allowed the FBI to guess the passcode through multiple attempts without erasing the iPhone.

The new information was then used to create a piece of hardware that helped the FBI to crack the iPhone's four-digit personal identification number without triggering a security feature that would have erased all the data, the individuals said. The researchers, who typically keep a low profile, specialize in hunting for vulnerabilities in software and then in some cases selling them to the U.S. government. They were paid a one-time flat fee for the solution.

The method the FBI allegedly used to break into the iPhone is similar in description to the tool that it had requested from Apple. Before finding an alternate way into the iPhone, the FBI had demanded Apple create a new version of iOS that would disable the passcode security features built into the operating system.

Apple was ordered to give the FBI software to disable the erase feature that would have wiped the iPhone after 10 incorrect guesses, eliminate the time added between entry attempts after the wrong passcode was entered, and create a way for the FBI to enter passcodes into the device electronically instead of manually.

The FBI did not need the services of Cellebrite "in this case," according to The Washington Post's sources, despite evidence the FBI signed a $15,000 contract with Cellebrite on March 21, the same day the Justice Department asked the court to postpone its imminent hearing with Apple. The tool acquired from the hackers did end up letting the FBI access the phone, leading the case against Apple to be dropped.

The U.S. government has not decided whether the method used to break into the iPhone will be shared with Apple, but FBI director James Comey has said the tool used to access the iPhone only works on a "narrow slice of phones" that does not include the iPhone 5s and later. Apple does not plan to sue to obtain the information.