New Delhi, May 12 -- Federal agents are investigating the deaths of six people thought to be immigrants found inside a shipping container at a Union Pacific rail yard near the border with Mexico in Laredo, Texas, on Sunday as a "potential human smuggling event."

A Union Pacific employee found the bodies of six people inside a shipping container Sunday afternoon, said Jose Baeza, the Laredo Police Department public information officer.

Dr. Corinne Stern, the Webb County medical examiner, is conducting autopsies and completed one for a 29-year-old Mexican woman who died of hyperthermia, or heat stroke.

"I've ruled that an accidental death," she said, adding that she believes the others also died from heat stroke but could not rule on the...