A driver who saw a girl shivering by a semi-trailer stalled on the side of the road led to the grim discovery of 46 people who died in a suspected botched human smuggling attempt near San Antonio, The Monitor has learned.

The victims suspected to be migrants died while trapped inside a tractor-trailer that passed through a Laredo Border Patrol checkpoint Monday afternoon, according to information shared with The Monitor.

The trailer crossed through the North Laredo checkpoint around 2 p.m. and was found near San Antonio on Monday evening in an apparent smuggling attempt, according to a source not authorized to speak officially on the matter.

New information shared with The Monitor indicates a driver noticed an injured girl in need of help close to the trailer. After 911 was called, emergency responders opened the trailer and found bodies inside and some people still alive but in need of medical attention.

As of Monday evening up to 46 people are believed to have died. About 17 were injured and sent to hospitals nearby in various conditions. The ages of the victims are unknown, but minors are suspected to be among the group.

The semi-trailer was found abandoned on the side of the road without a driver. However, a witness reported a pickup truck that was later found when the trailer’s license plate address was traced to a location in San Antonio, according to a source. Two people were taken into custody.

Border Patrol agents assigned to the Laredo Sector, Cotulla, Texas station and Laredo Sector Intelligence Units are responding to the scene, according to an internal communication sent by CBP. 

An official response from U.S. Customs and Border Protection was sought and remains pending.

Homeland Security Investigations is investigating the incident as a potential migrant smuggling attempt in South Texas, according to the source.

Editor’s note: This story has been updated with more information about the circumstances of the discovery.