Six bodies were discovered inside a boxcar in Laredo, Texas on Saturday, authorities said, with the cause of death and circumstances of the case not immediately known.
Laredo sits directly on the U.S.-Mexico border and ranks among the busiest land-freight crossings in the country, handling billions of dollars in commercial cargo annually.
Officials had not publicly identified the victims or confirmed whether the deaths were being treated as criminal. No cause of death had been released as of Saturday evening.
The News could not independently confirm late Saturday whether federal law enforcement — including Customs and Border Protection or the FBI — had assumed a role in the investigation.
Border crossings in Laredo have previously been linked to migrant smuggling operations in which individuals have died in sealed freight compartments in extreme heat.
Local and federal officials are expected to release further details Sunday as the investigation continues.