The death toll after an abandoned tractor-trailer was found in San Antonio continued to grow Wednesday, reaching 53 people in what officials are calling likely the deadliest smuggling incident in U.S. history. 

Of the 53 people who died, 40 were identified as male and 13 as female, according to the Bexar County Public Information Office. Most of them have been identified as migrants. By Wednesday morning, officials said they potentially identified 37 of the victims and were working to confirm their identities through methods like fingerprint analysis.

The tragedy occurred at a time when huge numbers of migrants have been coming to the U.S., many of them taking perilous risks to cross swift rivers and canals and scorching desert landscapes. Migrants were stopped nearly 240,000 times in May, up by one-third from a year ago.

What do we know about the victims?

Bodies of passengers who authorities said suffered from heat stroke and heat exhaustion were carried out of the truck Monday and spread out in body bags on the ground.

The victims who have been identified were from Mexico, Guatemala and Honduras, according to U.S. Immigration and Customs Enforcement. Rubén Minutti Zanatta, Consul General of Mexico in San Antonio, said he believes 27 of the victims who died were Mexican nationals, adding that he’s received dozens of requests from Mexicans searching for missing relatives who may have been among those found in the truck.

The death count was the highest ever from a smuggling incident in the United States, according to Craig Larrabee, acting special agent in charge of Homeland Security Investigations in San Antonio.

PREVIOUS REPORTS:Dozens dead after abandoned trailer filled with migrants found in San Antonio.

How many people were hospitalized?

Eleven individuals remain hospitalized as of 12 p.m. Wednesday, according to U.S. Immigration and Customs Enforcement.

José Luis Guzmán Vásquez, 32, from San Miguel Huautla in the southern state of Oaxaca, was among the survivors, said Aida Ruiz García, director of the Oaxacan Institute for Migrant Attention.

Identifying victims may prove difficult, experts say

Experts told USA TODAY that identifying those who died may be a long, complicated and costly process, not only because multiple countries are involved, but because families of migrants seeking relocation to the United States may be fearful of coming forward.

“It’s pretty much detective work,” said Bexar County spokesman Tom Peine.

Part of what makes identifying migrants difficult is that frequently those seeking entry into the United States may not want to be identified because they don’t want to be sent back to their original country, so they may carry no documents at all, or carry false documents indicating that they are, for example, from Mexico rather than Guatemala to end up closer to the border, said Lori Baker, a forensic anthropologist and professor at Baylor University in Texas.