THE LOCAL SHERIFF THOUGHT THE MURDER WOULD LEAD INVESTIGATORS BACK TO MEXICAN DRUG CARTEL VIOLENCE. HE DIDN'T RXPECT A U.S. BORDER PATROL AGENT TO BE AMONG THOSE ARRESTED.

 the local sheriff thought the murder would lead investigators back to Mexican drug cartel violence. He didn't expect a U.S. Border Patrol agent to be among those arrested.

When Franky Palacios Paz was found naked and decapitated floating off South Padre Island,

the local sheriff thought the murder would lead investigators back to Mexican drug cartel violence. He didn't expect a U.S. Border Patrol agent to be among those arrested.

The Texas Tribune is taking a yearlong look at the issues of border security and immigration.

This part of the project focuses on U.S. law enforcement corruption, which has undermined efforts to secure the border. Sign up to get story alerts.

SOUTH PADRE ISLAND — It looked like a crab trap floating in the calm waters of Laguna Madre, just off South Padre Island.

At least, that's what the man who spotted it while boating with his two daughters would tell police.

But when he poked the floating mass with a pole, he discovered otherwise. He dialed 911 and told the South Padre Island Police Department what he'd found: "a headless body floating in the bay."

Blood was still dripping from the neck when Cameron County Sheriff's Deputy Ulises Martinez arrived, he would later report.

It looked to him like the head "had been cut off with one swift motion with a fine sharp cutting instrument."

The grisly discovery came at a busy time on the island. It was March 16, 2015, the frenzied start of Texas Week, when thousands of spring breaking college students descend on Padre to guzzle from beer bongs and get rowdy.

Maybe one drank too much, fell in the water and collided with the wrong end of a propeller-driven barge?

That was an early theory, but Cameron County Sheriff Omar Lucio, with more than a half-century in law enforcement, sensed something more sinister.

"We're just across the border from Matamoros," he said. Investigators couldn't find the man's head, and there were other suspicious cuts on the body.

Mexican drug cartel payback often comes at the end of a fine, sharp cutting instrument, Lucio observed.

"It's just kind of the way that they handle people," he said. "They take revenge that way."

Luckily, the body still had hands. Using a portable fingerprint reader from U.S. Homeland Security Investigations, police quickly matched the prints to Jose Francisco Palacios Paz.

Before he was found naked and decapitated days after his 33rd birthday, Palacios Paz — "Franky" to his friends — worked at Veteran's Tire Shop in Edinburg, one county over.

In no time, authorities came to suspect that tire repair wasn't the only thing going on there.

It's where they think Franky — about to rat out a drug trafficking operation with links to the powerful Mexican Gulf Cartel — met his end.

Over the ensuing weeks, the investigation led authorities on a meandering journey through the Gulf Cartel's internal bloodletting, featuring tales of a supposed double-crossing cartel hitman, a U.S.-

born narco turned folk legend and a major mafia capo nicknamed "Commander Pussy" now locked up in a federal prison in Houston, Texas.

And by last summer, they had arrested four of Franky's tire shop associates on murder and drug trafficking charges.