A police informant says he was told that the driver was “unaware” the air conditioning had failed.
The suspected driver of a lorry where 53 migrants died from heat in Texas did not know that the air conditioner had stopped working, an informant says.
According to charging documents filed in federal court, Homero Zamorano did not know of the issue. Officials say he was found hiding nearby the truck.
The Texan is one of four people charged in the deadliest human trafficking incident in US history.
Several children found in the lorry are still being treated in hospital.
Mr Zamorano, 45, and alleged conspirator Christian Martínez, 28, are accused of sending text messages to each other about the smuggling operation both before and after the truck was discovered in sweltering temperatures.
A confidential government informant working for Immigration and Customs Enforcement and Texas police told officials that the two had spoken after the deaths were reported.
Mr Martínez allegedly told the informant: “The driver was unaware the air conditioning unit stopped working and was the reason why the individuals died,” according to court documents.
The documents add that the informant and Mr Martínez were standing within several metres of each other when the conversation with the driver took place.
Mr Zamorano was found hiding in bushes near the truck. Mexican officials say he initially tried to pass himself off as one of the survivors.
He was arrested when surveillance photos showed him driving the truck past a US Border Patrol checkpoint in Laredo, Texas, on Monday. According to one Texas congressman, he was high on methamphetamine when he was caught.
Both men face the death penalty if found guilty of smuggling and conspiracy charges.
Two other men accused of being involved, Juan Claudio D’Luna-Méndez and Francisco D’Luna-Bilbao, have been charged with firearms possession and with being in the US illegally. Both are Mexican citizens.
Mexican authorities say a total of 67 migrants were inside the lorry, while prosecutors in San Antonio have put the number at 64.
On Friday, the Bexar County medical examiner’s office said it had “conclusively identified” six of the 53 victims from Monday’s incident.
In addition, 42 “potential identifications” have been made. Five remain unidentified.
The victims have so far included 27 Mexican citizens, as well as 14 Hondurans, seven Guatemalans and two Salvadorans.