So far, more than 250 people have been arrested, including two from Tucson.
Investigators are scrolling through social media, as they try to piece together the events leading up to the attack.
Another tool that investigators are expected to use are so-called geofence warrants.
They are a sort of a 'digital dragnet' in which Google provides police information regarding all location-enabled smartphones that were present within a specific area, during a certain time-frame.
"People need to understand that when you carry your cellphone on you, you are being tracked at all times," said Mark Rumold, attorney with the Electronic Frontier Foundation.
The Digging Deeper team uncovered at least three geofence warrants filed by Tucson Police detectives who are now working to solve crimes ranging from armed robbery to murder.
"What we look at is when is the right time to obtain a geofence warrant, and is it necessary? I understand there are a lot of concerns not just within the community, but nationally about the utilization of that type of information, and so we take those concerns seriously," said Tucson Police Lt. Corey Doggett, who is the commander of the Violent Crimes Section.
However, groups like the American Civil Liberties Union and the Electronic Frontier Foundation worry that geofence warrants could potentially be abused.
"These warrants essentially compel Google to go through the location information of tens of millions of its users," Rumold said.
Lt. Doggett says Tucson Police only use geofence warrants for investigations related to the most violent of crimes, and after all leads have been exhausted.
"It requires two warrants from a judge, so two different authorization points from an external source that says I grant you authority to obtain that data." Lt. Doggett told the Digging Deeper team.
Geofence warrants are far from perfect.
In 2018, an Arizona man was arrested for a murder he didn't commit, based on information from a geofence warrant. Those charges were later dropped.
Several recent court cases have also called into question whether the warrants are constitutional in the first place, or if they violate the Fourth Amendment.
For now, the F.B.I. won't confirm what investigative tools it's using in this case, including geofence warrants.
Meanwhile, the number of geofence warrants by law enforcement continues to increase. On average, Google receives about 180 requests for location history information each week.