Six people were found dead inside a cargo train boxcar in a Texas city along the southern border on Sunday, officials said.
The bodies were found in a Union Pacific train at a rail yard in Laredo, around 160 miles south of San Antonio, just after 3:30 p.m. local time, said Jose Espinoza, a public information officer with the Laredo Police Department.
The circumstances of their deaths are unknown, said Laredo police spokesperson Joe Baeza, according to CNN affiliate KGNS, and an investigation is underway.
Union Pacific operates across the border and is the only railroad that services all access points into Mexico, according to the freight company’s website.
Temperatures on Sunday afternoon in Laredo were in the low-mid 90s, though it’s unclear whether heat was a factor.
Union Pacific said it was saddened by the incident and is working closely with law enforcement to investigate.
Laredo police said they received a call around 3 p.m. from an employee at the Union Pacific rail yard, KGNS reported. The bodies were discovered during a routine rail car inspection, police said. No survivors were found.
CNN has reached out to Laredo police for more information.
“It’s a very early phase of the investigation. There’s not a lot to reveal right now,” Baeza said, KGNS reported.
The immigration status and ages of the deceased are not yet known, Espinoza said.
US Customs and Border Protection referred CNN to the Laredo Police Department, saying “The incident remains under investigation by Laredo Police Department and Homeland Security Investigation and Texas Rangers.”
CNN has reached out to the Department of Homeland Security, HSI and the Texas Department of Public Safety.
“It’s a very unfortunate event,” Espinoza told CNN. “It was too many lives that were lost.”
This story has been updated with additional information.

