Nearly half of former president Donald Trump's supporters who gathered Jan. 6 to hear him complain the election was stolen marched to the U.S. Capitol at his direction -- where some of them stormed inside in a violent attack that left at least five people dead.
A source provided the New York Times with a data set tracking the smartphones of thousands of Trump supporters and others in the area that day, and it showed about 40 percent of the phones tracked near the rally stage on the National Mall were also pinpointed near the Capitol as the deadly riot played out.
Although the data contained no names or phone numbers associated with the phones, the Times was able to connect dozens of devices with their owners -- including Ronnie Vincent, a pest control business owner from Kentucky who posted photos of himself at the Capitol on his own Facebook page but soon took them down.
"There is no way that my phone shows me in there," Vincent told the Times.
But, the reporters said, it did -- although not all location data is precise enough to determine whether Vincent actually went inside, as he claimed on social media but walked back in a call with the newspaper, or just got near the Capitol, as his since-deleted Facebook posts show.
"Location companies can work with data derived from GPS sensors, Bluetooth signals and other sources," explained reporters Charlie Warzel and Stuart Thompson. "The quality depends on the settings of the phone and whether it is connected to Wi-Fi or a cell tower. Issues like population and building density can sometimes play a role in the quality of the data."
The data set given to the Times shows that Trump supporters traveled along major highways from all over the country to Washington, D.C., stopping along the way at gas stations, restaurants and motels, and then returned home along those same routes.
The location data also included a unique ID for each user tied to their smartphone, which allowed the reporters to match that anonymous ID to personal information -- including real names and birthdays -- within seconds.
"In the hands of law enforcement, this data could be evidence," the reporters note. "But at every other moment, the location data is reviewed by hedge funds, financial institutions and marketers, in an attempt to learn more about where we shop and how we live."
Law enforcement may not even need that data to build cases against the insurrectionists and rioters, because so many of them recorded incriminating video of their activities or discussed plans for the siege on the social media platform Parler -- whose data was leaked afterward.
But military agencies purchase and then use those data sets without a warrant, and private companies do, too.
"While some Americans might cheer the use of location databases to identify Trump supporters who converged on the Capitol, the use of commercial databases has worrying implications for civil liberties," Warzel and Thompson wrote. "The American criminal justice system is set up for a judge or jury to determine whether, in fact, Ronnie Vincent broke any laws on Jan. 6. But the data leads us directly to him, and in the hands of law enforcement officials — or rogue employees of the company that collected the data — it could narrow their search for participants and offer clues about their activity."