By Amy Silverman
By Olivia LaVecchia
By Monica Alonzo and Stephen Lemons
By Chris Parker
By Michael Lacey
By Weston Phippen
Martinez later told detectives he'd bumped into his girlfriend, Nicole Foster, on his way home to get firewood and beer. She corroborated that account, but added that she'd assumed Martinez was calling it a night. He wasn't.
Not everyone was thrilled to see the agent in the desert.
Patty Jacobo says Posada made a snide comment when Martinez pulled up to the party site at an alarming rate of speed.
He said he hoped Martinez had scratched his 1993 Chevy King Cab because he was acting like a big shot, as usual. The agent parked, turned on his car stereo and started a campfire.
Beer flowed. Laughter and music bounced off the nearby hills. One reveler climbed atop an old windmill that stood nearby; the others thought it was a foolish stunt.
Jacobo says she noticed how close Martinez was standing to the fire. He's gonna burn himself, she whispered to Eddie, who replied in Spanish that he didn't care.
"I tried to cover his mouth, and I said, 'Be quiet, he's a Border Patrol,'" Jacobo says. "He said, 'Every time he drinks, he goes around looking to argue with everyone and wanting to show them his guns.
'"But apparently no one who survived the night saw Martinez display his weapons. In fact, a few eyewitnesses say Martinez and Tapia seemed to be getting along--singing along with Sixties songs and acting like old pals.
By about 3 a.m., the party was on its last legs. The woman who had come with Tapia left with girlfriends. Posada's pals also took off, leaving the pair and Mark Martinez alone.
Nobody was alarmed when Posada and Tapia failed to come home. They were flighty types who thought little of leaving on occasion for parts unknown.
But Friday became Saturday, with no signs of the two men.
On Saturday night, a group of teens drove to the desert to do what people have been doing there for years: Drink beer.
Their reverie was interrupted by a dreadful stench. Though they were only a few hundred yards away, the teens didn't see Sergio Tapia's car, which was parked in a shallow swale.
Early the next evening--Sunday, August 7--the teenagers returned to the desert to find the source of the potent odor.
It was about 6 p.m. A storm approached from Mexico. The teenagers wandered around until Tapia's Nissan came into view. Someone looked inside the car and saw a body. A second body was lying face down in the dirt, about 30 feet from the car.
The youths rushed back to Douglas and flagged down a cop. Because the murder site was outside city limits, the case belonged to the Cochise County Sheriff's Office.
It was pouring by the time detectives arrived at the crime scene.
There they found a markedly decomposed body in the Nissan leaning, face up, against the rear passenger door. The driver's window was open. The autopsy would show that Sergio Tapia had been shot once in the right temple.
The body on the ground was that of Eddie Posada Jr. He had been shot once through the left eye at close range. Indentations in the dirt indicated Posada had been kneeling when the killer shot him.
The victim's feet were crossed, which would make detectives wonder whether Posada had been forced to assume a standard Border Patrol apprehension pose--subject kneeling, feet crossed, hands behind the head.
Word travels in Douglas faster than a monsoon thunderhead. One of the men who'd been at the desert party with the victims returned to the site, telling detectives that a Border Patrol agent named Mark had been at the party, and had been the last person seen with Posada and Tapia.
About two o'clock Monday morning, sheriff's detectives decided to talk with the agent.
It would be the first and only police interview with Mark Martinez.
The man sitting at his dining-room table facing the two sheriff's detectives was not a deep thinker. But Mark Martinez was fast on his feet, a quality that had served him well during his seven years with the U.S. Border Patrol.
His peers viewed the Texas native as gung ho, a five-foot-seven-inch man who made up for his lack of stature with bluster.
The agency had transferred Martinez to Douglas in the late 1980s. A divorce, he slipped into an off-duty routine of drinking beer, watching movies, working out, dating a succession of women.
In January 1994, Martinez bought a house on Cherokee Drive in Douglas for $68,000. Friends say he loved his job, loved the area and planned to stay as long as the agency let him.
Some inside the Border Patrol speak of Martinez as an upstanding agent and person. But his Achilles' heel, others say, is his short fuse, which becomes even shorter when he's drinking.
"He's one of those little short guys that don't like to be pushed," Arturo Gonzalez, a senior Border Patrol agent in Douglas, told detectives after the murders. "He's always chasing women and he's always drinking until late. He gets real feisty, and I don't like that.
"Vivid evidence of his temper came in January 1994, when a Douglas judge ordered Martinez to stay away from his onetime fiance. The judge did so after the woman petitioned the court for help. She wrote: "Mark Martinez came to my residence and began pounding on the windows, ringing the doorbell and then tried to forcibly enter through a window and tried to unlock the carport door. This is not the first time this has happened--he has done similar things a number of times during the last 12 months.