The two brothers had always worked together, ever since David, 34, persuaded his youngest brother to join him on the road as freelance pollsters for various companies. He had taught José how to approach interviewees and frame his questions.

It was no easy task. José, 30, could be quiet and withdrawn, the yin to David’s gregarious yang. José enjoyed odd hobbies, like making papier-mâché figurines and marshmallow lollipops, but held a deep reservoir of love for David, who was the eldest in the family, and David’s twin, 2-year-old sons. José was so devoted to the boys that David sometimes joked that he was the real father.

David, by contrast, was the kind of person who would take up all your time gabbing if you let him, Pablo recalled. David chose the job partly because it allowed him to talk to people and see the country. José loved it because it allowed him to work with his brother.

On the day they died, the brothers had arrived in Ajalpan around 9 a.m. They had come to this city of about 60,000 people for the firm Marketing Research and Services, polling residents about tortilla consumption by children. Often their work was like this, asking basic questions of populations on behalf of businesses collecting market data.

Though the job was standard enough, the context was not. The town was swirling in a tempest of fear. In the days before the pair arrived, social media brimmed with warnings about child abductions and admonitions to be on the lookout for strangers.

Just a few hours after the Copado brothers arrived, word began to spread about the two, dressed in slacks and collared shirts, carrying shoulder bags. By evening, a group of townspeople approached the pair outside a store.

The crowd demanded to know why they were asking about children. The brothers explained and produced identification. But the residents grew more aggressive, witnesses said, until the police arrived and took the brothers away.