The iCloud account password was changed remotely hours after the associated iPhone of one of the San Bernardino killers came under the possession of federal authorities.
In a court filing the Justice Department acknowledged the owner of the device used by Syed Farook was able to reset the password.
Federal official said the auto reset of iCloud account was executed by a country information technology employee and the investigators came to know about it after it had occurred and the employee acted on his own, without any orders of federal authorities.
According to Apple executives, the iPhone of the killer was in the possession of the government when reset of password was done.
Farook and his wife Tashfeen Malik killed fourteen people on December 2, 2015, in a deadly assault.
Meanwhile, Apple has refused to cooperate with the federal authorities in offering technological assistance to allow turning off of feature that erases data of a defuse if repeated attempt fails.
A legal fight between the federal authorities and Apple continues. A hearing on the matter is on March 22 in Riverside, California.
For the authorities the phone is valuable evidence as Farook used the device for months before the attacks to communicate with his wife and others.