The head of the FBI said Wednesday that the government had "purchased a tool" enabling investigators to access an iPhone belonging to San Bernardino gunman Syed Farook. 

The disclosure by James Comey in a speech at Ohio's Kenyon College was a departure from previous official statements, which had been vague in explaining the details of how the government broke into the phone last month.

The Justice Department had only said that a third party had "demonstrated" an alternate method of unlocking the device to the FBI the evening before federal prosecutors filed a motion to delay a court hearing on the matter.

"The people that we bought this [tool] from – I know a fair amount about them and I have a high degree of confidence that they are very good at protecting it, and their motivations align with ours," Comey said during a question-and-answer period following his talk.

Comey added that the technology only works on an iPhone 5C, the type of phone used by Farook. 

"This doesn’t work on [an iPhone] 6S, doesn’t work in a 5S, and so we have a tool that works on a narrow slice of phones," he added.

Neither the Justice Department nor the FBI could immediately provide further details.

The exact method the FBI used to access information on Farook's phone is a mystery that has puzzled Apple software engineers and outside experts alike. After the FBI hacked into the phone, Magistrate Judge Sheri Pym vacated her order compelling Apple to assist the FBI in hacking their phone, which also took away any obvious legal avenues Apple might have used to learn how the FBI did it.

A senior law enforcement official told The Associated Press last month that the FBI managed to defeat an Apple security feature that threatened to delete the phone's contents if the FBI failed to enter the correct passcode combination after 10 tries. That allowed the government to repeatedly and continuously test passcodes in what's known as a brute-force attack until the right code is entered and the phone is unlocked.

It wasn't clear how the FBI dealt with a related Apple security feature that introduces increasing time delays between guesses. 

At the time, Comey said with those features removed, the FBI could break into the phone in 26 minutes.

Farook died with his wife in a gun battle with police after they killed 14 people Dec. 2 in San Bernardino, Calif. The iPhone, issued to Farook by his employer, the county health department, was found in a vehicle the day after the shooting.

A senior FBI official told The Wall Street Journal Tuesday that investigators were still analyzing the phone and had not decided whether to disclose what they had found. 

Fox News' Matthew Dean and the Associated Press contributed to this report.