Speaking at a security forum in London, Comey elliptically referred to the cost of breaking into the iPhone as being more than the total he will earn in the remaining seven years of his 10-year term as the bureau's director. Comey earns $183,000 a year.
"We paid a lot," Comey said. "But it was worth it."
The FBI has not disclosed the identity of the party who helped it crack into the device. A law enforcement official has said that investigators found nothing of significance on the phone used by Syed Rizwan Farook, who died in a gun battle with police on Dec. 2 after he and his wife, Tashfeen Malik, killed 14 people and wounded 22 others.
In February, the Justice Department obtained a court order compelling Apple to help investigators bypass the device's security features in a way that wouldn't automatically erase its contents. Apple refused and the ensuing court fight generated a heated controversy that pitted the Justice Department and other law enforcement officials against privacy advocates and major technology companies who fear creating "backdoors" into their products.
The FBI last month abruptly dropped the case when it was approached by an unidentified third party that had found a way to circumvent the phone's security features. Comey and other top Justice Department officials credited publicity surrounding the court clash with spurring outside groups to try to hack into the phone.
Comey told an audience at a security forum hosted by the Aspen Institute on Thursday that relying on a similar strategy to break into other encrypted devices was not a viable long-term solution.