The suspected driver of a lorry in which dozens of migrants died during a human trafficking attempt in Texas was allegedly under the influence of methamphetamine, a US politician told Reuters.
Fifty-three migrants died in blazing heat, making it the deadliest such trafficking incident on record in the US.
US Representative Henry Cuellar, a Democrat whose district includes the eastern part of San Antonio, told Reuters on Thursday that Mr Zamorano, 45, was found to have had the powerful synthetic drug in his system.
Mr Cuellar said he had been briefed by US Customs and Border Protection (CBP) but did not know how authorities made that determination. A CBP official told Reuters that Mr Zamorano had tested positive for the drug.
Mr Zamorano appeared in federal court in San Antonio on Thursday where human trafficking charges against him were read. If convicted, he faces a maximum sentence of life in prison or the death penalty and a fine of up to $250,000, he was told.
He was accompanied by public defender Jose Gonzalez-Falla, who declined to comment on the case. US Magistrate Judge Elizabeth Chestney said Mr Zamorano would be held in custody until his next hearing on July 6.
Officials described finding the lorry's rear door ajar with bodies stacked inside that were hot to the touch. In nearby bushes, officers discovered other victims, some deceased.
They found Mr Zamorano hiding near the victims and escorted him to a local hospital for medical evaluation, prosecutors said. Mexican officials said he had tried to pass himself off as one of the survivors.
The lorry had been carrying migrants from Mexico, Guatemala, Honduras and El Salvador, and was found in a desolate, industrial area near a motorway on the outskirts of San Antonio, near the US-Mexico border.
Temperatures in the area that day had soared above 39ºC. Authorities called to the scene found no water supplies or signs of a working air conditioning unit inside the back of the lorry.
Prosecutors allege Mr Zamorano conspired with Christian Martinez, 28, who was also charged with a human trafficking offence.
Mr Martinez on Monday sent a picture of a load manifest for the lorry to Mr Zamorano, who responded by saying, “I go to the same spot”, a federal investigator wrote in a court filing Wednesday.
Mr Martinez repeatedly messaged Mr Zamorano in the hours after but received no reply, wrote Nestor Canales, a special agent with the investigations division of the Immigration and Customs Enforcement's (ICE).
Mr Martinez sent messages including “Call me bro” and “Wya bro”, meaning “where you at”, Mr Canales wrote.
A confidential informant for ICE and the Texas police spoke with Mr Martinez after the incident, Mr Canales wrote.
Mr Martinez told the informant that “the driver was unaware the air conditioning unit stopped working and was the reason why the individuals died”, Mr Canales said.