Thirteen undocumented immigrants from Mexico and Honduras are being held as material witnesses in the federal death penalty case against a truck driver who allegedly smuggled dozens of people in an overheated tractor-trailer, leading to 10 deaths, according to federal court records.

Nine of the potential witnesses, including one woman, their faces drawn and arms cuffed, appeared in U.S. District Court on Wednesday in San Antonio. U.S. Magistrate Judge Elizabeth Chestney told them that they were not facing criminal charges but would remain in federal custody, be assigned a lawyer, and be asked to give a video deposition in the case in late August.

Four other immigrants appeared in court as possible witnesses earlier in the week.

The court appointed Michael McCrum, a former federal prosecutor, to represent the immigrants. In a telephone interview, McCrum said he planned to meet with the immigrants soon to determine if they would serve as witnesses in the federal case. He said he thought federal officials should provide them visas, instead of taking their testimony and deporting them.

"They should be treated as people,¨ McCrum said. ¨So often we think of their situation as just chips in a monopoly game … These are people with real problems, with real needs who have been victimized."

The immigrants, wearing matching blue prison scrubs, listened to a simultaneous translation of the court hearing and nodded somberly as they answered the judge´s questions.

James Matthew Bradley, Jr., the truck driver charged in the case, has waived his right to a bond hearing and will not appear in court on Thursday as previously scheduled, according to the court clerk's office. Bradley is charged with smuggling immigrants for financial gain resulting in death, and is being held without bail.

His defense lawyer, Alfredo Villarreal, did not immediately respond to a request for comment.

In a separate news conference Wednesday, Reyna Torres, the consul general of Mexico in San Antonio, said 13 Mexican citizens who were on board the truck remain in area hospitals, some are in serious condition.

Of the 39 victims who remained on the scene when authorities arrived, 34 are Mexican citizens, she said. Those who are not hospitalized have been transferred into federal custody. Two immigrants remain unidentified, she said.

Two are minors, she said. One is hospitalized, another is in federal custody.

The immigrants hailed from a dozen states in Mexico, including 10 from the state of Aguascalientes. Seven of the 10 people who died were of Mexican descent.

Witnesses have told authorities that more than 100 passengers were crammed into the stifling hot cargo bay before the truck stopped in a Walmart parking lot late Saturday night. When the doors were opened, many passengers reportedly fled in SUVs and on foot.

Torres said U.S. officials are working with the consulate to allow relatives in the United States and from Mexico to visit immigrants in the hospital.

Torres said they have been able to identify migrants using fingerprints in Mexican government databases, taken when their citizens seek a passport or other forms of government identification. She urged immigrants who may have fled the truck to get in touch with the consulate if they need assistance.

"This is a very sad moment," she said. "I am very grateful for the support that I have received."