The FBI has found no links to foreign terrorists on the iPhone of a San Bernardino, California, terrorist but is still hoping that an ongoing analysis could advance its investigation into the mass shooting in December, U.S. law enforcement officials said.

For instance, geolocation data found on the phone might yet yield clues into the movements of the killers in the days and weeks before the attack, officials said. The bureau is also trying to figure out what they did in an 18-minute period after the shooting.

Investigators knew all along that finding important clues on the phone, which was a work phone owned by San Bernardino County, was a long shot, officials said, but they wanted to make sure their inquiry was thorough.

“For the FBI to competently investigate a mass murder that happened in the United States, we believed we had to use all lawful tools to find out whether there was evidence on that phone that either shed more light on what these two killers had done,” FBI Director James B. Comey said at Ohio’s Kenyon College last week.

Last month, a third party – professional hackers who hunt software flaws to sell – demonstrated to the bureau a method for unlocking the Apple iPhone of Syed Rizwan Farook, one of the killers in the attack that left 14 people dead.

The method proved successful, officials said, but it has not so far turned up anything that sheds new light on the motive of Farook and his wife, Tashfeen Malik, or whether they were plotting other attacks or had other associates.