SAN ANTONIO (AP) — All but six of the 53 migrants found dead or dying in a tractor-trailer in Texas last week have been identified, officials said Wednesday.

The Bexar County Medical Examiner's Office said 22 of the dead were from Mexico, 19 were from Guatemala and six were from Honduras.

The migrants were found in an abandoned trailer June 27 on a back road on the edge of San Antonio. The alleged driver of the truck was due in federal court Wednesday for a detention hearing.

The dead included a 13-year-old and 14-year-old from Guatemala and two 16-year-olds from Mexico, the medical examiner's office said.

One survivor of the journey, a 20-year-old from Guatemala, told The Associated Press that smugglers had covered the trailer's floor with what she believes was powdered chicken bouillon, apparently to throw off any dogs at checkpoint.

The truck was carrying 73 people in all when it was found June 27. Federal prosecutors say four people have been arrested in connection with the discovery of the truck, including the driver.

Guatemala's investigation into the smuggling networks is moving slowly, said Stuardo Campo, the prosecutor who is overseeing the case.

"So far we believe that there were four smuggling structures involved in this case," Campo said. His office is working with counterparts in Mexico and the U.S. Department of Homeland Security.

Guatemala's Foreign Relations Ministry has said that the majority of the 22 victims from that country were from the San Marcos department that borders Mexico.

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Associated Press journalist Sonia Pérez D. contributed to this report from Guatemala City.