Texas man pleads guilty to firearms offense linked to Mexico murder, kidnapping case

A Texas man pleaded guilty to smuggling a firearm that authorities linked to the deadly kidnapping of four U.S. citizens near the border in Mexico, according to the U.S. Attorney's Office for the Southern District of Texas.

Roberto Lugardo Moreno Jr. admitted to purchasing the pistol and then taking it to Mexico for the Gulf Cartel, the Wednesday statement from the U.S. Attorney's Office said.

"These weapons often contribute to fueling the violence committed by drug cartels, which drastically affects communities both in Mexico and in the United States," said Acting Special Agent in Charge Craig Larrabee of Homeland Security Investigations San Antonio. "This investigation and prosecution highlight the fine work federal border security agencies perform each day, often behind the scenes and often unknown to the public."

After the four Americans arrived in Matamoros, Mexico, in March, "unidentified gunmen fired upon the passengers in the vehicle," the U.S. Embassy in Mexico City said at the time. Two of the Americans were killed, and the other two were found days later in Mexico.

Five alleged members of a powerful Mexican cartel were charged with aggravated kidnapping and murder a day after the Gulf Cartel allegedly took responsibility for the kidnapping. The five men were found tied up near a pickup truck, and a handwritten note, purportedly written by members of the cartel, was found placed on the truck's windshield.

"We have decided to deliver those involved and directly responsible," the note said, presumably referring to the five men found tied up at the scene.

Moreno is expected to be sentenced in August. He faces up to 10 years in federal prison and the potential for $250,000 in fines.

The public defenders' office handling Moreno's case did not immediately respond to a request for comment from ABC News.

ABC News' Anne Laurent contributed to this report.