Rizwan Farook and his wife killed 14 people in San Bernardino in December.
Apple had been resisting a court order issued last month requiring the firm to write new software to allow officials to access Rizwan Farook’s phone.
But iPhone management declined to respond the court order. At the time, Apple said it did not know how to gain access, and said it hoped that the government would share with them any vulnerabilities of the iPhone that might come to light.
A court hearing with Apple was postponed at the request of the justice department, while it investigated new ways of accessing the phone.
The FBI has managed to unlock the iPhone of the San Bernardino gunman without Apple’s help, ending a court case, the US justice department says.
But officials on Monday said that it had been accessed independently and asked for the order to be withdrawn.
They were later shot dead by police. US officials said Mr Farook’s wife, Tashfeen Malik, pledged allegiance to the so-called Islamic State on social media on the day of the shooting.
