It should have been a victory for Tennessee narcotics policing. Drug task force agents see a car zoom past on Interstate 65 South in Robertson County — prime conditions for the kind of pretextual traffic stop that could lead to a drug search. Indeed, a search of the late-model Ford sedan reveals that the two Hispanic men from Dayton, Ohio, are drug mules who've been paid a pittance to risk transporting a half-kilo of heroin down a known drug corridor.

The driver, Luis Alberto Ruiz, and his passenger and cousin, Gerardo Ruiz, are arrested. Five hundred bucks isn't much incentive to cover for anybody, so Gerardo leads the agents to Rogelio Villar, the Nashville dealer who was the dope's alleged destination. Some 500 grams of a nasty drug didn't make it to Music City, and the operation couldn't have gone more smoothly. Case closed, right?

Instead, Lt. Shane Daugherty, a team supervisor with the 17th Judicial Drug Task Force and perhaps one of the most high-profile narcos in the state, now finds his own credibility in question. Meanwhile, the Ruizes are all but ready to walk out of jail as free men. With one ruling, federal district Judge Aleta Trauger rendered the evidence Daugherty discovered off limits and the prosecution's case against the cousins virtually unwinnable.

The message Trauger's memo sends to the agent and the Tennessee law enforcement community in general is clear: Have probable cause nailed down — or suffer the consequences in court. At issue is not whether one or both of the Ruizes were knowingly transporting heroin, but whether they were ever speeding in the first place.

If they weren't — and Trauger doesn't seem to buy Daugherty's assurances that he clocked them at 79 mph — then the stop was illegal, runs afoul of constitutional protections, and suggests the accused drug transporters were racially profiled (however accurate the hunch about stopping them might have proved). Worst of all, it invalidates in court nearly everything that occurred thereafter.

On Sept. 14, 2010, Daugherty and Special Agent Travis Childers watched the Ruiz cousins pass them on the highway. To Daugherty — who also sits on the board of the International Narcotics Interdiction Association, is a past president of the state Narcotics Officers Association and was once named the National Criminal Enforcement Association's Officer of the Year — it seemed strange that Luis' hands were fixed firmly in the 10-and-two position. He testified in court that the radar was on and that it clocked the sedan doing 79 in a 70 zone, so he pulled out of the median and onto the asphalt.

Daugherty gunned the Chevy Tahoe, hitting speeds of more than 100 mph in pursuit. In a narrative written two days after the arrest, Daugherty says he caught up to the sedan, pulled alongside and paced it at about 77 mph. He then dropped the car back behind Ruiz and hit the lights.

The dashboard camera in his SUV corroborates his story — to a point. According to undisputed testimony from a defense expert witness, the footage shows Daugherty pacing Ruiz, but certainly not at 77 mph. Judging by the speed at which the cars passed between the broken traffic lines, they were going 69 or 70 at best.

At an evidentiary hearing six months later, Daugherty's story changed. He now claimed he pulled alongside the car only to get a look at an object in the backseat, which later turned out to be a child's pink car seat. The pacing was actually done from behind, he testified. Trauger was dubious of Daugherty's belated about-face.

"It seems unlikely that Daugherty made such a significant error in a report written just two days after the stop, particularly because that account is consistent with the only available documentary evidence of the pursuit," Trauger writes. "It seems more likely that Daugherty really did pace the car while he was beside it, as written in the Narrative, and that he only later realized that the video showed that the Ruiz vehicle was not speeding."

It didn't help his case that the dashboard camera was set to permanently record everything after the activation of the emergency lights. As such, it includes footage only of the previous 30 seconds. Trauger seemed irked by the arbitrary configuration of the camera's digital video recorder, which basically assures that the actual justification — or lack thereof — for the traffic stop was not recorded. The radar wasn't hooked up to the camera either, which would have preserved for posterity the Ruiz cousins' speed.

Special Agent Childers — who, again, was in the Tahoe — wouldn't come near his senior officer's story. He claimed he didn't see the radar readout, which sits squarely in the center of the dashboard. He wouldn't even say he "assumed" Ruiz was speeding when Daugherty took off after him.

And Daugherty didn't do himself much of a service on the stand. The decorated veteran became emotional, attesting to the "sleepless nights" the defense's expert witness caused him.

Assistant U.S. Attorney Alex Little tried his best to salvage the terminally flawed case, stretching a recorded comment uttered in the back of the police cruiser into some sort of mea culpa. At issue was a phrase Gerardo said to Luis: "Ya estamos bien retrasados, buey."

According to the prosecution's translation, that means "We're really late now" — evidence they must have been speeding, as an admission that they were late and trying to make good time. By then, that $500 must not have seemed worth the trouble. But as the defense argued, and Trauger agreed, retrasados can mean "stupid" or "retarded," not late — in which case the phrase could be taken along the lines of, "We made a stupid mistake." Not an implausible thought from someone in the back of a cop car.

When reached for comment, Little and U.S. Attorney Jerry Martin wouldn't say for sure whether they'd appeal Trauger's decision, though they noted that it wouldn't affect their case against Villar. Neither Villar's nor Luis' attorney would comment. Gerardo's attorney didn't respond by press time.

Timothy Lane, director of the 17th Judicial Drugs Task Force — for whom Daugherty works — said he'd been told the U.S. Attorney's Office would appeal, but declined to specify his source. He characterized the decision as a "poor ruling," said Daugherty was not suspended from the task force, and declined to make him available for an interview.

It's a shame that a narcotics agent who by all accounts distinguished himself in his work could find it sullied by a single case. And none of this is to lament the trod-upon rights of beleaguered drug traffickers. But when a narcotics agent is posted on the highway, every traffic stop he makes is a pretext and a prelude to a drug seizure. The Constitution says that pretext has to be legitimate, not just to protect guys like Luis and Gerardo, but to shield us all from unreasonable searches and seizures.

Driving while brown simply doesn't cut it.

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