"Litigation between the government and Apple over the San Bernardino phone has ended, because the government has purchased, from a private party, a way to get into that phone, 5C, running iOS 9," Comey said.
It's likely that Israeli forensics company Cellebrite was the source of the tool.
"The people we bought this 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," he said.
The tool only works on a "narrow slice of phones" that does not include the iPhone 5S or newer devices. Notably, the FBI has yet to decide whether to provide Apple with details about the security flaw that made unlocking the iPhone possible.
"We tell Apple, then they're going to fix it, then we're back where we started from," he said. "We may end up there, we just haven't decided yet."