"Kate Westmoreland, an attorney and fellow at Stanford University's Center for Internet and Society, said there's a "whole tool kit" of digital information investigators can frequently obtain in crime investigations.
Smart phone activity is captured in a number of places: cell phone towers intercept people’s locations, emails are stockpiled on servers and contacts, call and text histories often live in archives held by wireless companies, pictures and recordings are often uploaded to the cloud.
The specifics of what the FBI has been able to obtain so far are unclear, but, Westmoreland said, generally law enforcement has a lot of options at their disposal.
"It's not like there is only one way to go about it," Westmoreland said. "You can find some of those same pieces in a couple of different locations. So whether some information you found particularly by unlocking the phone was the key to [the investigation] that's difficult to say."
While much of the phone's data likely exists in the ether, there are some things that may just live on a phone, said Rick Forno, a cyber security expert with the University of Maryland, Baltimore County.
Investigators could be after browsing data and encrypted communications, he said.
"Maybe any websites that [Farook] surfed on the phone that might point to a jihadi forum somewhere on the dark net or maybe some text files with names or information," he said.
But, Forno said, the FBI's request for the terrorist case should be closely examined for its ability to set a precedent for future breaches of privacy, as executives at Apple fear.
"A phone is a almost a digital archive of our entire lives,"Forno said."
Listen to the story at KPCC.