Two Mexican nationals at an address linked to the abandoned trailer truck where at least 53 migrants were found dead Monday evening in Texas have been charged with illegally possessing guns as federal authorities continue investigating the grim discovery.

Juan Claudio D’Luna Mendez and Juan Francisco D’Luna Bilbao were at a house in the 100 block of Arnold Drive in San Antonio, listed on the registration papers for the big rig that contained the bodies, which had been discovered abandoned in an industrial area of the Texas city, agents with the federal bureau of Alcohol, Tobacco and Firearms wrote in a criminal complaint.

Local police were staking the building at the address when they saw the D’Lunas get into a Ford F-250. Officers stopped the pickup truck to question the men after they began driving off, said the criminal complaint, which was filed in federal court Tuesday.

Officers said they obtained a warrant to search the house, and they found a shotgun, a rifle and three pistols divided among the men’s bedrooms. There was also a pistol in the F-250.

Neither man could legally possess guns because they allegedly admitted that they were in the US from Mexico on visas that had expired and which they had overstayed, agents wrote in their complaint. They jailed both D’Lunas on illegal weapons possession charges, and a judge ordered both to be held without bond until at least Friday, records show.

Either man could face up to 10 years in prison if eventually convicted as charged.

Agents as of Wednesday had stopped short of directly connecting the D’Lunas to the deaths of the migrants. But it’s clear they are suspected of other illicit conduct.

Authorities said three people whom police detained within hours of the bodies’ discovery were suspected of plotting to smuggle the migrants across the southern US border without permission.

One of the detained was the driver of the rig, who had pretended to be a migrant passenger. The two others were initially described only as Mexican nationals, which the D’Lunas are.

The attorney listed for D’Luna Mendez declined comment Wednesday. D’Luna Bilbao’s lawyer couldn’t immediately be reached.

At least 53 people found in the trailer of the rig at the center of the case have died, and 11 more have been hospitalized. It is believed to be the nation’s deadliest smuggling episode on the US-Mexico border, reigniting the longstanding debate about American immigration policies.

Officials believe the truck was carrying 67 migrants from countries such as Mexico, Honduras and Guatemala. Forty of the dead so far were male, and 13 were female, said the medical examiner’s office in Bexar county, which includes San Antonio.

The identities of fewer than 40 of the dead had been established as of Wednesday afternoon, authorities said, citing challenges in tracking down the names and relatives of people who furtively cross borders.

Eleven people were hospitalized with dehydration and other heat-related illness, having been in a trailer that lacked water and air conditioning as it traveled through temperatures approaching 100F (38C).

Texas’ governor, Greg Abbott, said the state’s public safety department would immediately begin adding more checkpoints for large trailer trucks on well-trafficked roadways in an effort to limit episodes like the one Monday.