Authorities in Laredo, Texas, near the US–Mexico border, have recovered six bodies from a freight train car. Police confirmed the number of deceased and said an investigation is under way.

Freight trains move massive volumes of goods between Mexico and the United States every day. Officials say some people attempting to enter the US via Mexico travel dangerously on top of or inside freight trains, and fatal incidents have been reported in the past.

In this case, investigators are examining whether harsh conditions inside the rail car—such as extreme heat and lack of ventilation—or accidents during unsafe travel contributed to the deaths.

Officials have not released the identities of the victims. The probe is also looking into how long the bodies were inside the train and whether any foul play was involved.

With severe heat prevailing in southern Texas, authorities are specifically assessing whether heat exposure played a role in the deaths.