California college student Anjali Banerjee was watching fireworks during a 2016 celebration on a seafront promenade in the French city of Nice when a man plowed a huge truck through the crowd, killing 86 people and wounding 200.

The University of California, Berkeley incoming senior ran through mobs of people to escape the chaos and later joined classmates to search hospitals and plaster the city with flyers of fellow students reported missing in the July 2016 terrorist attack.

She later learned three students were injured, and UC Berkeley junior Nicolas Leslie, 20, was among the dead.

Banerjee and several classmates have since turned their grief into a startup called Archer that builds digital tools to help journalists, investigators and human rights workers tackle terrorism, sanctions evasion, corruption and other global violence.

“In that moment, it was hard finding the correct information. It was hard even going to different police stations. It was chaos,” said Banerjee, who is from London.

The lack of official information following the terrorist attack by a Tunisian man led the students to self-organise and rely on locals to navigate the city as they looked for their missing friends. The militant Islamic State group claimed responsibility for the Bastille Day attack.

Collaborating with each other and with the people of Nice made the students realise they could create a space in the digital world to help others do the same in the fight against terrorism, Banerjee said.

The students built a free online platform that makes big data analysis and visualisation easy to access and that helps track people and companies that have been sanctioned by the United States (US) for crimes that include money laundering, corruption and terrorism.

They're still working to turn their data analysis tool into a for-profit company, but the startup has achieved some success. Amnesty International is using one of its tools, Archer Meta, to verify photographs of the crackdown by security forces against minority Rohingya Muslims in Myanmar's Rakhine state.

The tool identifies when and where the photographs were taken and can process 50 at once, unlike other readily available internet tools that upload one photo at a time and can pose a security risk, said Sam Dubberley, a researcher with Amnesty International.

“We get photographs in bulk from activists groups in Myanmar, and we have to verify they are true. But uploading one at a time can be mind-numbing, tedious work,” he said.

Archer Meta also offers an added layer of security by allowing users to analyse a photo's metadata without relying on an internet connection, Dubberley said.

“These tools are needed in human rights work, but they are prohibitively expensive to develop, and there is no money in it for tech companies to build them,” he said.

The group's data analysis tool helps those investigating terrorist financing cases, “but there is a broader community of people who can rely on our tools, including those looking into war crimes, sanction violations or environmental crimes,” said Alice Ma, a former UC Berkeley student who founded the startup with Banerjee and classmate Tyler Heintz.

Heintz was also in Nice at the time of the attack. They have since been joined by nearly two dozen other students, including several others who were with them in France as part of a month-long class and competition hosted by the European Innovation Academy, which focuses on tech entrepreneurship education.

Banerjee, a history major, had considered a career in foreign affairs but after what happened in France, she wanted to take immediate action.

Weeks before the attack, her friend Tarishi Jain, a UC Berkeley sophomore, was among 20 hostages killed at a restaurant by militants in Dhaka, Bangladesh.

“A lot of people all over the world exist in this kind of situation on the daily, and we thought it was time somebody suggested another way we could combat it,” Banerjee said.

Experiencing the France attack also pushed Heintz, a 20-year-old computer science major, to change his professional goals.

“Before Nice, I was very much on the traditional path of wanting to build the next app that a bunch of people would use for some reason but that doesn't actually change anyone's lives. But building an app that can help you transport your cat or dog just seemed so trivial,” he said.

What motivates Heintz and “a lot of us, is the idea that we can build products to help magnify the work of people trying to bring terrorists to justice,” he added.