The Mexican drug cartel attorney who was slain execution-style in Southlake last week had been a confidential informant for the U.S. government, law enforcement sources told NBC 5.

Juan Guerrero Chapa, 43, had worked for the Department of Homeland Security Investigations, secretly providing inside information on cartel operations to American investigators.

HSI is part of U.S. Immigration and Customs Enforcement.

Guerrero was gunned down at about 7 p.m. May 22 at the Southlake Town Square by a masked man who jumped out of the back seat of a white sport utility vehicle, police said. It was the first homicide in the upscale suburb since 1999.

The attorney had worked for top leaders of the Gulf Cartel, including former top boss Osiel Cardenas, who is now in prison in the United States.

It was unclear if his role as an informant may have leaked to the cartel, providing a motive for his killing. At least two U.S. trials of high-ranking Gulf Cartel members have concluded in recent weeks.

Guerrero, a Mexican citizen, his wife and three teenage children had been living in Southlake for two years, police said.

They had been living in the U.S. legally, according to ICE spokesman Carl Rusnok. High-level informants from Mexico or other countries are sometimes allowed to live in the United States as long as they are cooperating.

Rusnok had no comment when asked about Guerrero’s role as an informant. He referred questions to Southlake police.

Southlake police spokeswoman Kim Leach also declined comment.

Along with the FBI and the Drug Enforcement Administration, HSI investigates drug crimes.

With 6,700 special agents, HSI is the second-largest federal law enforcement agency. Only the FBI is bigger.

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