One of several men indicted in a smuggling operation that left 53 migrants dead after they were trapped in the back of a sweltering semitruck in San Antonio last year has pleaded guilty, authorities said.

The June 2022 tragedy -- which at the time was described as the deadliest human smuggling incident in US history -- left families grieving across Mexico, Guatemala and Honduras as authorities identified the dead from the abandoned truck.

Multiple men were later indicted by federal grand juries in connection with the smuggling operation, including 29-year-old Christian Martinez, of Palestine, Texas.

Martinez pleaded guilty Wednesday to multiple counts, including transportation of migrants resulting in death, transportation of migrants resulting in serious bodily injury and placing lives in jeopardy, the US Attorney's Office Western District of Texas said in a news release.

He faces a maximum penalty of life in prison during his sentencing, which is scheduled for January 4, the US Attorney's Office said.

CNN has reached out to an attorney for Martinez for comment.

Also charged in the case is the tractor trailer's alleged driver, Homero Zamorano Jr., 47, of Elkhart, Texas, according to the US Attorney's Office.

Martinez drove Zamorano from Palestine to San Antonio where Zamorano picked up the empty tractor-trailer and "loaded the migrants into the tractor trailer," the US Attorney's Office said, citing the indictment.

At least 66 migrants, including eight children and one pregnant woman, were loaded onto the truck, according to the Department of Justice.

Martinez and others "then coordinated, facilitated, passed messages, and made each other aware of the tractor-trailer's progress," the US Attorney's Office said.

Authorities were able to connect Zamorano and Martinez to the operation through surveillance footage and phone communications obtained through a search warrant, the DOJ previously said.

In addition to the 53 people who died, nearly a dozen others on the truck were hospitalized for heat-related conditions.

The refrigerated semitractor-trailer that was carrying the migrants had no visible working air conditioning unit, no sign of water inside and none of the passengers were able to get themselves out, San Antonio Fire Chief Charles Hood told reporters after the truck was found.