On today’s podcast we present the Introduction and Part 1 of Mongol, our exclusive new Crime Story series written and read by Molly Miller that tells the story of the tragic killing of a police officer and the complex search for truth and justice in the aftermath of his death.


It was the summer of 2019, and David Martinez was on trial for the murder of Pomona Police Officer Sean Diamond. The case was one of the first that Crime Story covered and at the outset it appeared simple: a coldblooded gang member had killed a cop. This tragedy fit the silent film that plays on the wall of the American subconscious. The good guys had fought the bad guys and the bad had left a bloody mark. Now the court would balance the scales. Justice would be served. But as my Crime Story colleagues and I watched the case unspool, we realized that our binary paradigm was eroding. We came to understand that this trial was part of a much larger story, one that informed how Deputy District Attorneys — on behalf of the People of California — framed their entire argument. Our research into th e events leading to the raid on David Martinez’s home offered us valuable context for what drove the prosecution’s strategy in pursuing this case. In the Deputy District Attorney’s presentation, this wasn’t just a case of a police officer being killed in the line of duty; this was an assassination committed as part of a gang’s war on law enforcement. Prosecutors sought to depict David Martinez as the embodiment of the battle between the Mongols Motorcycle Club and the federal government. The Mongols Motorcycle Club was founded in 1969 in Montebello, CA by a brotherhood of Latinx men who had been excluded from the Hells Angels. They called themselves “outlaws” and “one-percenters” – referring to a comment by the American Motorcyclist Association that 99% of motorcyclists were law abiding citizens, implying that one percent were not. Since those early days, the Mongols have grown in number. They now have chapters in nineteen states, stretching as far east as New York. They’ve also grown in criminal operations, having been convicted of illicit drug trafficking, money laundering, robbery, extortion, firearms violations, and murder — crimes that have been exposed by undercover ATF agents who infiltrated the club. The most notable of these undercover missions was Operation Black Rain, an ATF sting that resulted in the arrest of over 60 Mongols including then-Mongols president, Ruben Cavazos. Cavazos subsequently plead guilty to charges of racketeering and was sentenced to 14 years in prison. After his incarceration, Mongols Club members voted for his removal from office in 2008. The current president of the Mongols Motorcycle Club is David Santillan, a man who claims that the organization has changed its code of conduct to exclude drug abusers and criminals. ATF officials view Santillan’s public declarations about the club cleaning house as hollow words; they continue to treat the Mongols as a serious threat. In 2014, prosecutors even attempted to strip the Mongols of their trademarked logo (a Genghis Khan-like figure wearing sunglasses and riding a motorcycle). When interviewed, Santillan expressed that removal of the logo would be devastating to the club. Talking to reporters he said, “the patch is like a ring in a marriage, it symbolizes our loyalty and commitment.” Ultimately, the Mongols retained rights to their emblem under free-speech laws, but the ATF continued to pursue other means of eliminating the Mongols brotherhood. In 2014, local Los Angeles and Riverside County officials were also concerned about the Mongols’ illicit activities. Investigators feared that the Mongols were forcibly recruiting members of newer motorcycle clubs and compelling them to pay dues. In addition, law enforcement was busy attempting to curb the escalating violence between the Mongols, the Hells Angels and the sport bike club, G-Zer Tribe. Tensions were high after two incidents in which Mongols members were shot at or pushed off their bikes on freeways by other bikers, leaving one member killed, one paralyzed and several others wounded. Now officers feared that the Mongols were poised to retaliate. It was in the context of these parallel federal and local investigations that seven search warrants were served to suspected gang members’ residences on October 28, 2014 as part of a multi-agency operation to crack down on illicit club activities. One of those residences was the home of David Martinez.

Part 1

We all know there are two sides to every story. But in this story, there are two sides to a single door. It’s the wooden front door of the Martinez residence in San Gabriel, California. On one side of the door, a police officer was killed. On the other side, a man’s life changed forever. Outside of the door, on the evening of October 28, 2014, forty-five-year-old Pomona Police Officer Shaun Diamond was called to take part in a SWAT operation. Diamond was known as a devoted officer and a family man. At a young age, Diamond passed up opportunities to go to college to become an officer and provide for his daughter, Margo. Later, he gave his kidney to save his son, Kelly’s life when he was in need of a transplant. Now, on the force for 16 years, fellow officers described Diamond as “cuddly as a porcupine” but compassionate toward the community he served.” San Gabriel was outside of the Pomona Police jurisdiction, but it was common for the squad to assist neighboring cities when larger operations required more manpower. Diamond’s team was tasked with serving a search warrant to a house inhabited by David Martinez, an alleged member of the Mongols Motorcycle Club. The operation was considered high-risk due to the Mongols’ association with a wide range of criminal activities including the use of illegal firearms, meth trafficking, robbery, assault, and murder. Prior to arriving at the house, Diamond and his fellow officers set up traffic cones representing the Martinez home and property lines in the SWAT office parking lot. Under the glow of street lamps, the officer’s feet pounded the pavement, executing practice runs for maximum efficiency. When the movements were drilled into their bones, the squad packed up and headed to their target location. Upon reaching the Martinez home, several officers rammed the padlocked gate that led to the backyard of the property while others announced their presence and approached the front porch. Corporal Richard Aguiar and Officer Diamond breached the outer metal security door of the home with a push-pull device called a “ripram.” Diamond turned to discard the device as someone inside the home opened the inner, wooden door. Suddenly, a shot rang out and Diamond was hit in the back of the neck. The brutal injury killed him a few hours later.

Inside the door on the evening of October 28, 2014, thirty-six-year-old termite inspector David Martinez was working on inspection reports in the study. He had gotten a late start on the paperwork because he had spent the day helping his parents clean and operate the family laundromat. The last customer hadn’t left until 11 pm. Martinez lived in a two bedroom, Spanish style, stucco home with his parents, his sister, Brenda, who has Down syndrome, his wife, Sandra, and their two young children, Alyssa and David Jr. The living arrangement hadn’t always been this cramped. In the past, Sandra and Martinez resided in their own house with their children. But after a motorcycle accident kept Martinez from working for several months, financial strain brought the family back under the same roof. Martinez didn’t mind – it made it easier to help his aging parents. 

At 3 am, Martinez finished his reports. He climbed into bed with Sandra and was just about to fall asleep when he heard a banging noise that rattled the whole house. Martinez grabbed the shotgun that he kept by the side of his bed and ran to the living room where his parents and sister slept. Here the banging was even louder and the family’s four dogs were barking. Martinez saw his father, Arturo, by the door. He called out for his dad to wait, but Arturo had already turned the knob. The door opened to reveal the barrel of a gun pointed inside the home. Martinez aimed his shotgun.

In a split second a shot rang out. Arturo Martinez grabbed his arm and screamed, “they shot me! They shot me!” 

Outside, Shaun Diamond fell to the ground, blood spilling from his head onto the porch.

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