It was just after 2 a.m. on a Tuesday morning when Bob Lee called the police from a sleepy block near San Francisco’s Bay Bridge.

“Help!” he yelled into his phone, “Someone stabbed me.”

Lee was struggling to walk up a sparsely populated city street, according to surveillance footage captured at the scene. He attempted to wave down a white Camry with its hazard lights flashing but ended up collapsing on the ground when the car drove away. By the time the police arrived six minutes later, Lee was unconscious and bleeding uncontrollably from three knife wounds, one in the hip and two to the chest. He was rushed to San Francisco General Hospital where he was pronounced dead, the victim in a murder case that would captivate the nation. Lee was 43.

Everyone in the San Francisco tech scene knew Lee, a coder turned tech magnate who had helped build products worth billions, from the Cash App to Square’s payment terminal. His death led to a wave of finger-pointing by venture capitalists and entrepreneurs including Elon Musk who blamed it on liberal policies and homelessness.

The stabber, though, was not a stranger. Prosecutors say Lee was killed by another tech executive, Nima Momeni, who ran in the same circles as Lee. Police arrested Momeni on April 13 and charged him with Lee’s murder.

Fortune has spoken with more than a dozen people, including Lee’s and Momeni’s friends and coworkers and other people close to the two men, to piece together how their lives intersected and to trace the shock that has ensued.

Only Momeni now has the complete picture of what happened in those final minutes, but his lawyer, Paula Canny, cautioned that there are “multiple backstories.”

“Everybody will have to wait to hear what Bob Lee was doing,” she told Fortune.

The legacy of Bob Lee

Momeni’s and Lee’s lives started in very different places—Momeni in Iran, where he emigrated to the U.S. at a young age, and Lee in Missouri.

Born in 1979, Lee had been a water polo star at Lindbergh High School in an affluent suburb outside of St. Louis. He earned the nickname “Crazy Bob” for his ferocious play but gained a reputation for charisma and warmth, according to Nathan Wills, a fraternity brother from college. By the time Lee enrolled at Southeast Missouri State University, those aspects of his personality were front and center; people viewed him as a happy-go-lucky ball of energy endowed with a well of enthusiasm. He was also a budding tech phenom.

Wills recalls how Lee kept talking while on a road trip about a computer virus called Code Red terrorizing the world. Lee claimed to have come up with a solution to the virus, which had caused $2 billion in damages.

“There are people way smarter than you—hundreds, thousands of people working on this across the globe,” Wills remembers telling him. “You did not solve this.”

Undeterred, Lee spent the car ride expounding in meticulous detail about how he would patch the software. And, indeed, he wrote a program that users could implement to deflect it. He was invited onto a tech-focused TV program to talk about his solution, appearing in a polo with gel-slicked hair. The host referred to Lee as the “Code Red vigilante.”

Lee dropped out of college early. Mark Hatch, a friend he would later meet in the San Francisco “maker” community of do-it-yourself-focused hardware enthusiasts, speculated that it was because he wasn’t challenged enough. “He was a genius,” Hatch told Fortune. “How else do you describe it?”

Although Lee never became a household name like his fellow Missourian Jack Dorsey, who became his future boss at Square, Lee made outsize contributions during the heyday of the Silicon Valley tech scene. He published an influential manual on the coding language Java before contributing crucial work to Google’s AdWords empire. In 2010, Square recruited Lee to become its CTO, where he helped build the now-ubiquitous Cash App.

When Square went public in 2015, Lee posted photos from the New York Stock Exchange. Wills sent him a text. “Bobby, did you just become a millionaire?” Wills asked. Lee sent back a winky face.

The success didn’t go to his head. Hatch said that whenever they attended a party together, Lee would introduce him to every single one of his friends in the room as the cofounder of the maker movement. People wouldn’t even realize that he was the CTO of one of the most influential U.S. tech companies. “He didn’t wear his genius on his sleeve,” Hatch said.

Lee was an insatiable extrovert. As another friend, Tommy Sowers, put it, “He just wanted to suck the marrow out of life.” It was a habit Lee had in college, Wills recalls, staying up until four in the morning either working or going out. The habit lasted through his thirties and into his early forties, where Lee could outlast anyone who tried to keep pace.

Lee also loved to socialize in the Bay Area tech party scene, where a source said that drugs, including cocaine, were commonplace.

Lee’s professional and party lives sometimes crossed, like with Rooz Mohazzabi, a tech entrepreneur by day and DJ by night. Lee met Mohazzabi, who goes by “DJ Rooz,” at a developer conference for Android, soon bridging the professional relationship into a shared love of San Francisco’s underground rave scene. Lee asked Mohazzabi if he could set up Cash App at his shows.

“You’re working your ass off, working crazy hours. You need that release, to go be social and drink until four in the morning and hang out with friends,” Mohazzabi told Fortune.

Lee had two children, ages 14 and 17, but he separated from his wife in 2019 and moved to Miami during the pandemic with his father, continuing his lifestyle in perpetual motion. Whenever he came back to San Francisco, he took full advantage of his social scene, always wanting to see one more friend. It was during one of those long nights out that he met Nima Momeni.

The IT whiz

Nima Momeni never attained Bob Lee’s level of career success, but he built his own respectable tech fortune. He immigrated to the U.S. with his mother and sister, Khazar, and grew up outside of Berkeley. The family practiced Zoroastrianism, a pre-Islamic Iranian religion.

Momeni became an IT consultant, embedding at other companies where colleagues remember him as a pleasant and cordial worker.

“There were no red flags at all that would indicate that he would do something of this nature,” said Akash Sawhney, a product manager who intersected with Momeni for a few months at a tech startup in 2015.

Momeni got caught in a few problematic situations, however. Alameda County criminal records reviewed by Fortune reveal a litany of minor infractions, including a charge for driving under the influence of alcohol in 2004, and two charges for driving with a suspended license and possession of a switchblade in 2011. Momeni was sentenced to 10 days in jail and three years of probation for the suspended license charge, and the switchblade charge was dismissed. The San Francisco Chronicle also reported that Emeryville police had cited and released Momeni for misdemeanor battery, although prosecutors declined to charge him. At the time, an officer wrote that the victim thought that Momeni “may be bipolar because one minute he will be fine and the next he will go off for no reason.”

Another colleague, who worked with Momeni from 2006 to 2010 and asked to remain anonymous to protect their privacy, recalls Momeni talking about his suspended license. “If you know all of these priors, it’s less surprising,” the colleague told Fortune.

Paula Canny, Momeni’s attorney, dismissed the Emeryville case as “bullshit.”

“He was issued a citation, which means he wasn’t arrested,” she told Fortune. “It makes for a sensational headline, but it’s not of any import.”

Momeni’s sister, Khazar, also lived in the Bay Area, marrying a socialite plastic surgeon named Dino Elyassnia in 2013. They purchased a $2.7 million apartment in the glitzy Millennium Tower in 2016. The property is known for both its pricey residences and for being a (literally) sinking edifice, a source of schadenfreude in a city shaped by wealth inequality.

Nima Momeni also had a taste for some opulence, owning a boat, a BMW convertible that retails north of $50,000, and a rented live-work space in the Besler Building, an East Bay complex built in 1917 renovated to attract techies.

Sam Singer, a PR veteran who recently opened an office next to Nima Momeni’s, says that Momeni invited him for a tour of his workspace after Singer moved into the building. Momeni had been gracious and welcoming. “Our neighbor seemed like a very nice fellow and not capable of such a crime.”

Two paths cross

The details of how Lee and Momeni met are hazy, but several sources told Fortune that it was through broader social circles. In particular, Lee had a connection with Momeni’s sister Khazar, whom he met several years ago. Though court documents cast suspicion on whether the relationship was romantic, people close to both say they weren’t together. Khazar Momeni did not respond to a request for comment.

Court documents filed on April 14 by the district attorney and assistant district attorney for San Francisco begin to fill out the rest of the story. On Monday, April 3, Lee invited a close friend—identified as Witness-1—to an apartment in downtown San Francisco around 3:30 p.m. When the friend arrived, Lee was drinking with Khazar Momeni. The friend, who knew both of them, told police that Lee and Khazar Momeni had known each other for at least a few years.

Later in the afternoon, Lee and the friend left for Lee’s hotel near the Ferry Building, just a few blocks from San Francisco’s Bay Bridge. At that point, Lee had a phone call with Nima Momeni, where the friend said that Nima was asking whether his sister was doing drugs or anything inappropriate. Lee reassured him that nothing untoward had happened. The friend ended up leaving Lee around 12:30 a.m., now early Tuesday morning.

According to surveillance footage reviewed by police, Lee left his hotel for the Millennium Tower around 12:39 a.m., the sinking building where Khazar Momeni had an apartment with her husband, just a few blocks from Lee’s hotel. Nima Momeni had already been at his sister’s apartment for a few hours.

At 2:03 a.m., Lee and Nima Momeni entered an elevator together from the floor of his sister’s apartment, taking it to the lobby, and getting into Momeni’s BMW. As the court documents detail, Momeni drove them to a “dark and secluded” area nearby, parking the car. Footage captures the two men stepping into the night, with one suddenly moving toward the other before they separate. One man, who police identify as Momeni, walks south and stops along a fence, where police later recovered a knife. The other man, Lee, staggers north. The BMW speeds away. Lee would die in the early hours of the morning at San Francisco General Hospital.

After police recovered Lee’s phone, they found a text from Khazar Momeni.

“Just wanted to make sure your [sic] doing ok Cause I know nima came wayyyyyy down hard on you And thank you for being such a classy man handling it with class,” she wrote, “Love you Selfish pricks.”

Lee’s friends are left to speculate on what happened. Nathan Wills, his frat brother, thought that he was probably trying to diffuse the situation. “Bob is not a confrontational person,” he said.

The only certainty is the immense feeling of loss they now feel. For those who knew him, Lee was a singular person who could change the world while never losing his humility. His already prodigious impact was reflected in the torrent of responses precipitated by his death from every corner of the tech world. Some honored his legacy, like his onetime boss, Jack Dorsey, who wrote the news was “heartbreaking.” Others seized on the tragedy to complain about what “San Francisco has become.”

Hatch, Lee’s friend from the maker community, lamented how quickly his death became politicized, with his apparent murder seized either to decry crime in San Francisco or the myopia of its tech scene.

“It diminishes his memory,” Hatch said.

Momeni’s arrest just over a week later would shift the attention. Now the question is how the two men ended up on that shrouded block at 2:30 a.m. on a Tuesday morning. Prosecutors allege that the killing was premeditated, pointing to the fact that Momeni had brought a cooking knife, which police later found at the crime scene, and drove Lee to a remote location.

“This was a planned and deliberate attack,” they wrote.

On April 25, Momeni will be arraigned. If found guilty, he faces 26 years to life, according to prosecutors. As of April 22, his lawyer Paula Canny said that she’s still awaiting documentation of the prosecutors’ charges, including medical records, surveillance footage, and witness interviews. She said that Momeni will likely wait to enter a plea until they have time to review the prosecution’s evidence.

“People shouldn’t rush to judgment,” she told Fortune. “Sometimes in complicated, messy situations of people’s lives, it takes a little bit of a time to figure out what’s true.”

As the reality of Lee’s killing sets in, the cold bureaucracy of the legal system will begin. For Momeni, it will represent his last chance to provide answers to Lee’s loved ones.

“I just felt a different type of loss,” said Tommy Sowers, an Iraq War veteran who met Lee while running for Congress. “Sadness for his kids, and for his friends, and then this violent, selfish loss.”