Police let most Capitol rioters walk away. But cellphone data and videos could now lead to more arrests.

Phone records make determining the owners of these devices trivially easy. Congressional investigators and federal prosecutors can also identify devices and users who may have connected wittingly or automatically to congressional guest WiFi networks — unless rioters made a point of deactivating their devices or leaving them behind during the takeover.

The countless hours of video — much of it taken by the rioters themselves and uploaded to social media — also offers an ideal data set for facial recognition. Many scenes were captured from multiple angles, with good lighting, over several minutes. Few people wore masks. While facial recognition technology often struggles to reliably identify people with dark skin, the large majority of the Trump supporters who entered the Capitol on Wednesday appeared to be White.

“Some people were being very blatant and flippant about it, smiling for the camera — those people are going to be very easy to find,” said Doug Kouns, a retired FBI special agent and founder of the Indiana-based private-investigation firm Veracity IIR. “I worked with the bureau for a long time, and when I watched that play out I got the same hollow feeling in my stomach as on 9/11: How is this happening? They’re going to use every resource they can to bring these people to justice.”

Video of rioters walking away untouched after the takeover enraged many around the country hoping to see consequences for those who broke the law while apparently seeking to disrupt the certification of President-elect Joe Biden’s victory. The contrast was especially striking, many critics said, after the aggressive, heavily armed crackdowns against protesters in May and June after the killing of George Floyd.

But leaving the scene without arrest is not the same as escaping criminal charges. D.C. and federal authorities have made clear their determination to investigate the catastrophic security breakdown and prosecute many of those involved.

“This investigation has the highest priority of the Department of Justice. We have literally hundreds of prosecutors and agents working from three command centers on what is really a 24-hour a day operation. It is active, it is fluid, it is evolving,” said Principal Assistant U.S. Attorney Kenneth C. Kohl of Washington on Friday.

FBI Washington Field Office chief Steven M. D’Antuono said, “Just because you’ve left the D.C. region, you can still expect a knock on the door if we find out you were part of criminal activity in the Capitol.”

Privacy advocates have warned that such a dramatic event could prompt an expansion in the use of the surveillance technologies in a way that could erode civil rights. But the investigation highlights how government officials already have broad legal authorities to use them how they see fit.

Justice Department officials have said that federal investigators are using tools such as facial recognition to help analyze a weighty amount of photos, videos and other evidence. The FBI declined to comment about what investigative technology it might use.

But U.S. prosecutors, for example, were able to identify 15 security guards for Turkish President Recep Tayyip Erdogan who were allegedly involved in a melee in May 2017 outside the Turkish ambassador’s residence in Washington through the aid of videos taken of the incident.

The Capitol also has extensive security cameras constantly trained on key spots. Federal prosecutors charged and convicted Libyan militants who attacked U.S. facilities in Benghazi, Libya, in September 2012 by linking their phone calls and cell location information to individuals who were captured on footage breaking into and roaming through a diplomatic compound, images gathered by U.S.-government owned security cameras.

Efforts to get cellular, Wifi and video data could be complicated by the constitutional boundaries between executive-branch prosecutors and the Congressional leaders who have authority over the Capitol. But given the shared interest in investigating Wednesday’s incident thoroughly, that’s unlikely to be a serious barrier, said Stephen Vladeck, a constitutional law professor at the University of Texas. The goal for Congressional leaders will be to allow evidence to be collected without creating a precedent that could enable future surveillance of legislative business.

“It’s a soft separation-of-powers issue,” Vladeck said. “It’s about norms, not hard and fast rules.”

Amateur sleuths already have worked to identify those captured in publicly available video. An Instagram page is crowdsourcing this task, and investigative reporting group Bellingcat has requested video for cataloguing.

In some cases, people identified publicly already have lost their jobs or suffered other consequences, including arrest. One rioter who was photographed wearing his company ID badge in a lanyard around his neck was quickly fired. The Justice Department on Friday announced 13 charges against rioters suspected in the breach, which FBI director Christopher A. Wray said in a statement was “an affront on our democracy.”

The ability of law enforcement to use similar tools is significantly more profound because of the availability of cell-tower records and the ability to subpoena photos and video. The commercial-grade facial recognition technology available to police also can compare images to those in government databases, including from state driver’s license records and criminal files to dramatically increase the potential for clear matches.

Kouns said the Capitol takeover offered a “trove of valuable evidence,” especially because many people had captured themselves committing potential crimes and, in some cases, shared the evidence publicly.

And unlike with a typical bank robbery or shoplifting case, he said investigators don’t have to rely on grainy or distant surveillance-camera footage. Instead, the events were captured in countless smartphone photos, video live streams and location-tagged social media posts.

But Evan Greer, deputy director of the digital rights advocacy group Fight for the Future, said she worried that the use of facial recognition in “this very unique scenario” might help lionize a technology that is routinely deployed by police and immigration agents to surveil people of color.

“It’s always in these moments of crisis that people are more willing to accept government overreach,” said Greer, who drew a parallel to the bolstered surveillance infrastructure that followed the Sept. 11, 2001, attacks.

“Normalizing and glorifying these technologies will end up hurting the same people these far-right elements are trying to attack and harm,” Greer added. “If you really believe that expanding technologies like facial recognition will primarily be used to target groups like the Proud Boys, you haven’t been paying attention to history.”

Federal investigators routinely use facial recognition searches to identify or investigate criminal suspects, and a growing number of local police forces are beginning to deploy their own privately run software to pursue violent and low-level crimes.

The FBI’s software can scan through a database that includes more than 641 million photos of Americans’ faces, largely taken from jail mug shot photos, visa applications and driver’s licenses, according to a Government Accountability Office report in 2019. More than 390,000 facial recognition searches have been run by local, state and federal investigators over the last decade.

The FBI has tweeted photo collages of rioters’ faces and has asked the general public for any “tips and digital media” that captured the riots and violence during the Capitol siege.

But the authorities are also using much simpler methods to find and charge insurrection suspects. In one criminal complaint filed Thursday, a D.C. police investigator said she arrested one man who had invaded the Capitol because she recognized him from a photo on The Washington Post’s website.

Devlin Barrett contributed to this report.