The families of four U.S. citizens who were murdered by gangs in Mexico have filed a lawsuit against the British multinational bank HSBC, claiming that the bank willfully let the cartels in question launder billions of dollars via its institutions.

The suit was filed in Brownsville, Texas, the home of immigration and customs agent Jaime J. Zapata, who was murdered four years ago this month by members of the Zetas cartel, the Brownsville Herald reported.

Zapata’s family cosigned the suit, which alleges that HSBC readily assisted the gangs, “disregarding the fact that said funds would be used to support the Mexican cartels and their terrorist acts against Mexican and U.S. citizens,” and can thereby be held partly accountable for the murders.

The suit addresses the grisly murders of three other Americans, The Guardian reports: Lesley Redelfs, a U.S. consulate employee who was four months pregnant, and her husband Arthur, who were shot down as they left a child’s birthday party; and Rafael Morales Valencia who was kidnapped after his wedding ceremony and then tortured and asphyxiated alongside his uncle and brother.

HSBC, which has pledged to combat the lawsuit, has a history of controversial transactions involving Mexican gangs. In 2012, it wrote a check for $1.9 billion to end a criminal investigation surrounding potential violations of U.S. sanctions laws and the laundering of nearly $900 million in cartel cash.

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