They were nabbed seven months later by the kind of digital footprints people increasingly leave without even realizing it. Law enforcement authorities have used all kinds of social media -- like Facebook and Instagram -- to track down people.
This time, it was Nunn's music listening habits that did her in.
Webber said a tipster had spotted recent activity from Nunn on music streaming service Spotify and alerted law enforcement. He scoured the Internet for other evidence of Nunn and Barr's movements, eventually filling out 12 search warrants for records at different technology companies. Those searches led him to an IP address that traced Nunn to Cabo San Lucas, Webber said.
Nunn, he said, had been avidly streaming television shows and children's programs on various online services, giving the sheriff's department a hint to their location.
(Spotify said in a statement that it cooperates with law enforcement authorities in criminal investigations and provides information "when compelled by valid subpoenas, court orders or search warrants.")
On July 7, Mexican authorities deported the family to the United States. The girls were reunited with their fathers. And Nunn and Barr were charged with felony counts of custody violations and unlawful flight from law enforcement.
Barr and Nunn do not have attorneys listed in a federal charging database, and they could not be reached for comment.
"As technology gets better and more companies come out, there are more opportunities to go get search warrants and figure out where people are," said Webber, who hadn't heard of Spotify until he was tipped off to Nunn's activity. "It’s becoming more and more of an investigative tool for us."
This is a classic case of "information asymmetry," said University of Washington law professor Ryan Calo, meaning when companies, government agencies or police departments have more information about your online habits than you even realize is out there.
"There's an enormous underestimation of your digital footprint," Calo said. "You might not realize how much your data is being stored, but you also might not realize how many parties have access to it. Think about all the uses to which this information can be put."
Webber, in this case, did just that.
"Not every company stores this information," he said, "but the ones that do is another chance for us to gather intelligence."
But Calo says the size of someone's online footprint depends on much more than their own activity.
What if someone spots you and tweets about you (like a group of Washington Post employees did when VEEP and Seinfeld star Julia Louis-Dreyfus showed up in the newsroom Tuesday)? What if someone takes a photo of you and posts it online (again, something we did with JLD)?
Or in Nunn's case, what if an app you're using notifies others of your activity, even as you were trying to stay off the grid?
"Maybe the Australian tourist taking photos of the block you’re on doesn’t know what’s going on, but if your face is on there, the police can find you," Calo said.
And beyond the police, the social media universe can find you as well. When Wired reporter Evan Ratliff tried to disappear for a month in 2009, social media users -- regular people without the search and seizure rights of law enforcement or the data-gathering techniques of large tech companies -- banded together to try to find him. They did. It took 23 days.
"If people are motivated to find you, they can use social media to do it," Calo said. Average people tracking you down online is scary perhaps. But it's nothing compared to the tools government has at its disposal.
"If the government is motivated to find you, it can scour the Internet and chances are, they’re going to find you," he said.