Two undocumented immigrants from Mexico are facing capital murder charges after allegedly fatally shooting an off-duty Border Patrol agent and wounding his father during a South Texas fishing trip.

Willacy County Sherriff Larry Spence said investigators Gustavo Tijerina, 30, and Ismael Hernandez, 40, tried to rob Agent Javier Vega Jr. and his family on Sunday while fishing near Santa Monica.

Hospital officials didn't immediately return a message Tuesday on the condition of Javier Vega Sr. of La Feria, while Homeland Security Secretary Jeh Johnson said in a statement Tuesday that the younger Vega was a veteran of the Marine Corps. He served in the Border Patrol for six years.

Tijerina and Hernandez were arraigned Tuesday afternoon and were ordered held without bail after being charged with capital murder, attempted murder and other lesser charges.

Police sources told FoxNews.com that the two men have been arrested and deported numerous times – one was arrested no fewer than four times for entering the U.S. without documents, while the other had been deported twice.

Spence said the two suspects were likely connected to cartels and had told police that they knew they had killed someone, but did not know it was a border agent.

They claim to have been involved in other incidents, this means you’ve got stolen vehicles going into Mexico,” he told Fox News. “Everything is going to be cartel-related, there’s a connection somehow.”

The Sheriff said this was not the first time there has been border violence in Willacy County, but it’s the first time someone has been killed.

The Associated Press contributed to this report.

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