On April 21, 1978, Border Patrol agents Frank Lugo and Jose Gamez Jr. drove their truck down a ranch road outside Eagle Pass and settled into their evening shift along the Rio Grande. They planned to lie in wait for illegal immigrants near a check gate in an irrigation canal. Swift and deep, the canal was the first hurdle for crossers after the river, and the gate was like a catwalk across it. Separated by about forty feet in the darkness, agents Lugo and Gamez intended to jump the first group that walked between them. It was a sound plan, but something went wrong. Though stories vary about what exactly happened, while Lugo was chasing a group of immigrants, his partner Gamez vanished.

The gantlet of trails along that stretch is difficult to navigate during the day, let alone in the dark. Agents searched throughout the night, but the grim discovery of Gamez’s corpse didn’t come until mid-morning, after the irrigation canal was drained several feet. They speculated that he had probably lost his footing while pursuing the immigrants across the narrow canal gate and fallen into the water below. Yet the following week, an autopsy found that Gamez had been struck on the head three times and strangled. Suddenly, supervisors realized that the search party had trampled through a crime scene. Even more unsettling, the last person known to have seen the murder victim alive was his partner, and Lugo’s story didn’t add up.

In South Texas, Gamez’s disappearance made headlines for days, a few of them hinting that the killer could have been Lugo. It didn’t help that he seemed to change his story each time he told it. He contradicted himself about the events leading up to the encounter with the immigrants, about the direction they came from and ran, and about the last place he’d seen Gamez alive. But what could Lugo’s motive have been? No one knew.

And no one knows. The case, one of many unsolved murders on the border over the years, still gnaws at agents who knew Gamez and Lugo. They can’t understand why it was never solved. Though Lugo has never been arrested or indicted in connection with Gamez’s death, he was the lead suspect for a number of years in an investigation conducted by the FBI. That case ultimately went cold, with no conclusion. A separate administrative investigation by the Immigration and Naturalization Service, which at the time maintained jurisdiction over the Border Patrol, sustained an allegation of “inattention to duty” but not an allegation that Lugo’s actions had “resulted in or contributed to the death of Gamez.”

The INS stopped short of firing Lugo, but the incident still threw the protective bond of the badge into question. Some agents believed that he was unfairly scapegoated. Some had grave questions about his role in the crime. Lugo, for his part, denied any involvement whatsoever. In fact, the central effort of his adult life has been convincing people that he is innocent. He wrote an unpublished book titled “The Exoneration.” In 1982 he and his wife sued the FBI and the INS for $21 million, alleging that the investigations had put pressure on him “at every turn to confess to actions and/or crimes he did not commit.” The case was dismissed. If he is innocent, Lugo’s life has been a second tragedy, a slow death weighed down by suffocating stress and disappointments. But is he? After thirty years, what happened is still a mystery.

Lugo and Gamez both came from large Spanish-speaking families in South Texas border towns, but that’s where the similarities end. Growing up in Laredo, Gamez traveled often with his parents for migrant farmwork. Lugo was raised around field work too, but his father owned trucks, organized laborers, and was involved in local politics, a full-contact sport in his hometown of Donna.

The two men followed different paths into the Border Patrol. Gamez decided to join after chatting with agents while fueling their trucks when he worked at a gas station in Laredo. Lugo came in after a stint in the Army. He was drafted in 1967 and sent to Vietnam, but halfway through his one-year tour, he returned home to be near his sick father. He would finish the second half of his military obligation as a lifeguard at Fort Sam Houston. The war marked a turning point in Lugo’s life. When he came home to Texas, he was nervous, his thoughts drifted, and he kept to himself, said his older brother, Roberto, who later became the first Hispanic mayor of Donna. Lugo was suffering from post-traumatic stress disorder (he still receives government disability payments for the condition). But he fulfilled his goal to graduate from college, earning a marketing degree in 1971 from what is now the University of Texas-Pan American, in Edinburg. He landed a job in a state welfare office, married in 1973, and a few years later, on a whim, took the Border Patrol exam and passed.

Gamez was placed in Eagle Pass in 1976. George Baxter, who graduated at the top of Gamez’s academy class and was also sent to Eagle Pass, remembers Gamez as a prudent, quiet agent, one who took notes and drew maps of the areas he patrolled in Maverick County. Lugo cut a different figure. He was opinionated and outspoken, especially on the subject of inequalities between Anglo and Hispanic agents. But former colleagues described him as a misfit, whose lavish storytelling about war and women was part of his persona. “Most of the time I would just tune him out,” recalled agent Joe Mendez, of Dallas, a friend of Lugo’s, who retired in 2004. “One thing, it was Vietnam, then working somewhere else. Then, about the fourth or fifth time around, he’d be back at Vietnam again with a different story, and you would be, ‘Frank, nobody would believe these stories you are trying to push out.’ ”

Gamez and Lugo teamed together on several shifts, but they didn’t get along well. In 1980 Gamez’s widow told INS investigators that her husband didn’t trust Lugo enough to walk in front of him. He was someone who often made bizarre comments. “On one occasion,” she recalled, “[Lugo] asked Joe what he would do if someone came behind you and tried to kill you.”

On the night in question, the two agents started their shift at 4 p.m. According to Lugo, a group of crossers appeared after dark. The agents nestled into their hiding spots, about forty feet apart on a trail by the canal. At some point, Gamez, closest to the approaching group, fired a warning shot, a violation of policy. He yelled for the immigrants to stop, but four or five took off sprinting. Lugo rushed toward the ruckus, but later said that in the commotion he could not clearly determine where Gamez was. This was one of several key details he would contradict. The immigrants split up and quickly scattered. Crossing the canal gate, Lugo searched a cane-covered strip of land that buffered the Rio Grande. He came back to the canal crossing with nothing. No immigrants. No Gamez. He eventually climbed back up to a lookout point where the truck was parked. He flashed the lights and honked the horn. He yelled out for Gamez. He fired his pistol, also violating policy, to get Gamez’s attention. Nothing.

Lugo did not immediately report the disappearance. He would later explain that he had assumed Gamez would turn up and didn’t want to embarrass him. But finally, at 11:35 p.m., just before the end of the shift, the radios of the other agents on duty in the area began chirping. “We had some wets come over the check gate,” Lugo said. “Some went upriver and some went downriver. [Gamez] went downriver, and I haven’t been able to locate him. I’m gonna have to go look for him.”

Twenty-two minutes later, Lugo was on the radio again, this time with a slightly different account: “I went to look for him. He went upriver on the river side of the canal, and I went downriver for some wets, and I come back, and I haven’t been able to find him yet.”

Agent Baxter, Gamez’s friend from the academy, was the first to show up and scour the area. Lugo told him several different stories. First he recounted hearing a splash in the river. Then he said the splash was in the canal, about one hundred yards away. First he claimed the immigrants had been walking from the highway side of the canal toward the check gate, which Baxter knew from experience to be unlikely, since it would have needlessly exposed them. Then Lugo said they’d been coming from the river side of the canal. As more agents arrived, Baxter observed that Lugo was telling each of them a slightly different story. Still, at that point, everybody figured Gamez was merely lost. Supervisors told Lugo not to mention that Gamez had violated agency policy by firing a warning shot. They didn’t want his image to be tarnished when he reappeared.

Meanwhile, as they combed through the thickets, agents detained several undocumented immigrants. Following routine procedure, they returned the immigrants immediately to Mexico. Later, agent Ramon T. Juarez gave a sworn statement in which he declared, “I would sure like to have those ten illegal aliens we found laid up on the river. They were scared, they knew something had happened . . . Lugo talked to them. I saw him talking to them.” A group of five immigrants caught in Brackettville, 46 miles north of Eagle Pass, told authorities they’d crossed the canal at the same spot at around the same time, but they weren’t held for questioning.

Since most of the initial search was limited to areas Lugo had described, he was effectively in control of it, a fact that rankled some. Several days later, Jack L. Richardson, the deputy chief patrol agent of the Del Rio sector, concluded in a memo recapping the night: “There can be no doubt in my mind that Border Patrol agent Frank Lugo lied to me at the scene and concealed material facts from me which would have aided and assisted our officers and the Mexican officers in the conduct of this search operation.”

The FBI assumed command of the investigation. Lugo was stripped of his weapon and remanded to administrative duties in the Eagle Pass office, pending the outcome. When the FBI homed in on him as its prime suspect, the writing was on the wall for many of his peers. They assumed that he’d been AWOL during the murder, frightened and unable to defend his partner, or an eyewitness to the hideous deed, or, perhaps, the murderer himself. Lugo agreed to two polygraph tests, both of which were inconclusive. But later, in a deposition for his federal lawsuit, he said that he had taken an antianxiety drug before one of the tests, which can distort the results. Lugo’s credibility diminished when he told the FBI that on the night of Gamez’s disappearance, he had found a bag of clothing in the brush and thrown it into the canal to avoid paperwork. Finally, he was called to testify at a federal grand jury in Del Rio, where a government prosecutor tore into him. In “The Exoneration,” Lugo recalls the prosecutor accusing him of being a liar and proclaiming that his “hands and feet [were] lethal weapons.”

Lugo blamed the autopsy and the media for his woes. According to his book, he told the grand jury, “I am sick and tired of the way I have been treated. I have been considered guilty until proven innocent. Damn that autopsy. There’s no way Joe could’ve been murdered. I wouldn’t have let it happen to him or anyone . . . Joe Gamez forgot about safety, and now I have to pay the price.”

Lugo remained on administrative duty in the tiny Eagle Pass office, but he resigned after two and a half years due to what he referred to as his “mental and physical condition.” Though the INS investigation had concluded that the evidence didn’t prove Lugo’s actions had resulted in or contributed to Gamez’s death, the other agents were shunning him. He was grinding his teeth down flat. He was hospitalized and medicated for depression.

A few years after leaving the patrol, Lugo found a job with the post office. He spent all his spare time working to clear his name. One of his two daughters recalls that during her childhood, Lugo was always hammering away on his book. His federal lawsuit stalled, but he kept trying to get compensation, sometimes acting as his own attorney. He filed open-records requests with the FBI and the INS and contacted Hollywood screenwriters, book publishers, the Commission on Civil Rights, the Equal Employment Opportunity Commission, then attorney general Janet Reno, various congressmen, and the U.S. Supreme Court.

Meanwhile, throughout the eighties, FBI investigators continued to work their case. They persuaded Lugo to undergo a marathon hypnotism session. They attempted to contact some of the immigrants who had been caught and released during the search for Gamez. A promising lead came in 1981, when an undocumented Mexican immigrant in the Chicago area told an informant that just a few years earlier, he had killed several people, including “a guard,” while crossing the border near Del Rio. The FBI made several attempts to find him, but it’s not clear if he was ever questioned. Access to many case records was restricted to protect the investigation, making it difficult, even now, to determine what exactly investigators found. The most recent available document, dated 1987, states that agents “will attempt to verify recapture” of an unnamed person of interest in Reynosa, Mexico. In 1988, ten years after Gamez was killed, the case was closed. The FBI had run out of leads.

Retired FBI agent Fritz Bohne was one of several agents assigned to the case. He told me the investigation was especially difficult because there was so little physical evidence. I asked him if his colleagues at the bureau thought Lugo had killed Gamez. “It was on everybody’s mind,” he said. “But if you can’t prove it, you can’t charge him with it.” The agent who ran the INS investigation, James Lucas, of El Paso, is more direct. Today, at 76, he still believes that Gamez was not killed at the check gate and dismisses Lugo’s explanations. “He knows exactly what happened,” Lucas told me. “I strongly believe that, because what he says happened did not happen.”

A persistent theory among those who have followed the case is that while Lugo was not the murderer, he might know who was, that some of his relationships were questionable. Lugo’s closest friends during the years he lived in Eagle Pass were a well-known Piedras Negras attorney, Vicente Lafuente Guereca, and his wife, Eloina. The Guerecas were godparents to Lugo’s youngest daughter. Five years ago, Vicente was gunned down on a Coahuila highway. Mexican police investigated the incident as a killing possibly related to drug trafficking.

Lugo is now 62 years old. In 2005, when I was a reporter for the San Antonio Express-News, he contacted me, asking for an opportunity to tell his side of the tangled story. We spoke on the telephone a few times, and I read a great deal about the case. Looking at the facts, it was hard not to wonder if Lugo might have had something to do with Gamez’s death. But why? And if he was guilty, why had the FBI investigation and the Del Rio grand jury failed to bring him to trial?

One day, I went to see Lugo at his beige-brick McAllen home, in the hopes that a visit might help me understand what had happened that night. Lugo answered the door dressed only in dark blue shorts, his gray hair combed perfectly. He welcomed me into a suburban-style living room with a large television, a prominent photo of a group of soldiers in Vietnam, and a glass frame full of medals and ribbons. His wife, bedridden since 2004 after a stroke, was in a back room.

As we talked, Lugo lounged on a sofa. I quickly realized what investigators meant about his being hard to follow. His thoughts seemed to bounce in every direction. Sometimes he closed his eyes and scanned the inside of his skull while he spoke. One minute he was telling me about how his partner’s death had helped him discover who he really was, the next minute he was rambling on about the definition of “truth” according to Sherlock Holmes. All of a sudden he scampered away like a barefoot child looking for a toy, returning moments later with a tray of pills for sleep, diabetes, depression, anxiety, and his heart. “This is my life,” he said.

His light brown skin was highlighted by the dark mail-carrier tan line around his neck; his bare chest was marked by a six-inch vertical scar from a heart surgery. “I don’t want to make my life complicated,” he told me. “I’ve managed to survive.” He showed me a laundry-basket-size archive of deposition transcripts, sworn statements, and court petitions and a briefcase full of old government memos written by agents and supervisors. It was all very neatly organized. A cardboard box cradled his 156-page manuscript. A red folder was titled “The Manipulation of the Media.” A green folder had a large sticker on it with these typewritten words: “Our generation of Hispanics went through hard times just to merit our piece of a dream. My life has not been easy, but without divine help, I would have not made it this far. The Exoneration is a legacy destined to be billed as: The Greatest Corrido Ever Written. The story just happened, all I did was tell it in words.” Lugo clings to his small archive as if it holds a key to the old case that has somehow been overlooked or ignored. But the bitter reality is that unless someone else comes forward, he will always have to live under the burden of being the only person with a story to tell about what happened on the night in question.