Willie McCoy knew his life could end in an instant.

The 20-year-old rapper wrote verses about police harassing him in California, the legal system labeling him as “dangerous”, and the fact that “one false move” could “end” someone like him. “I was guilty until I proved I’m innocent,” he rapped in one song.

Police in Willie’s hometown of Vallejo never gave him a chance to prove his innocence. On the evening of 9 February, six officers approached the young man who had been sleeping in his car at a Taco Bell and fired a barrage of bullets into the vehicle, hitting him with an estimated 25 shots in just four seconds, killing him on the spot. The department later claimed that when Willie awoke, it appeared he had “moved his hands downward” toward a handgun.

Play Video 1:59 Friends speak out about the police killing of Willie McCoy – video

Willie’s loved ones, who filed a wrongful death claim on Thursday before a Friday memorial service, have called it an “execution by a firing squad”, and the death has sparked outrage across the globe. The brutal killing has also shaken the Bay Area rap community where the artist known as Willie Bo was rising in prominence with his group FBG, which stands for “Forever Black Gods”.

On a recent afternoon, his longtime music collaborators, which included numerous relatives, gathered in a small music studio in east Oakland, and for the first time since Willie’s killing, listened to some of his music.

“Last time they pulled me over, they ain’t get shit!” two of them recited in unison, playing a recording on one of their iPhones of a recent Willie lyric.

“Police always harassing him, and he always overcoming that,” said Damariee Cole, Willie’s 28-year-old nephew, whose artist name is BooBooMane. “He was a targeted person … The music was about the hardships he overcame.”

“It hits us different every day,” said Levonte Cole, a 26-year-old cousin and artist known as Pay Me, who said he scrolls through his phone and pauses at Willie’s number, wishing he could call. Some songs, he said, were too painful to hear. “I just start crying.”

Facebook Twitter Pinterest Friends and collaborators of Willie McCoy at a music studio in Oakland, California. Photograph: Talia Herman/The Guardian

“They took a leader from us. When Willie was in your presence, you was honored to be around him,” added BooBooMane.

Willie’s friends and family described him as energetic and deeply loyal, a young man who was dedicated to building a career and life around music, who seemed so close to breaking through. While trying to remember him as he lived, some said they were haunted by thoughts of how he died. And those who viewed him after the killing said they were unable to escape the image of his face and body – completely unrecognizable and riddled with bullet holes.

‘They left him like an animal carcass’

The call came around midnight on Saturday 9 February: Willie had been shot in a parking lot. Marc McCoy, Willie’s 50-year-old brother, rushed to Vallejo, an East Bay city about 30 miles from San Francisco. A cousin who had called didn’t have much information, and Marc and other relatives initially thought Willie may have been caught up in street violence or that police had identified the wrong person.

Before they arrived from Oakland, they got the news that it was Willie, and he was gone. They spent the final 15 minutes driving in a state of shock.

When they arrived, Willie was lifeless on the ground, surrounded by officers, who had set up a wide perimeter blocking access to the crime scene. They soon learned it was police who had killed him. Officers were immediately hostile and rebuffed each of the questions asked by Willie’s brothers and cousins who made it to Taco Bell. Could they identify Willie? No. Could they see his body? No. Why was he killed? Nothing.

Facebook Twitter Pinterest David Harrison, a cousin who helped raise Willie. He rushed to the scene on the night of the shooting. Photograph: Talia Herman/The Guardian

“They told us to leave the area,” Marc recalled one evening a few days after the killing.

“They left him out there like an animal carcass … like a dog that got run over by a car,” said David Harrison, Willie’s 48-year-old cousin, who helped raise Willie and also rushed to the scene that night. “The way they was nonchalant, the way they spoke to my family after what we knew they had just done, it tore me up.”

The family said police never contacted them. But the department eventually began pushing out its official narrative through the local media. At 10.36pm, Taco Bell employees called 911 reporting a man “slumped over” in the driver’s seat at their drive-through.

A civil rights lawyer said she had never in her entire career seen a more horrifying sight

Two officers were dispatched for a “welfare check” and found the driver unconscious in the front seat, with the car on, according to police.

“He’s passed out … We need another unit,” one officer said, according to dispatch audio.

Officers claimed they saw a handgun on his lap, though the department has not released any body-camera footage. Eventually, six policemen surrounded the vehicle with guns drawn and all six unloaded their guns on him.

A witness video filmed from a distance captured what sounded like a sudden burst of fireworks.

After firing a series of shots that were likely deadly, the policemen then shouted commands: “Let me see your hands! Put your hands up!”

“All officers are okay,” one police official said on the dispatch recording. “He’s non-responsive.”

Five days later, the family was granted permission to see Willie’s body.

William Harrison, Willie’s great uncle, unzipped the body bag. No one else could bring themselves to do it.

“Everything that hit him was a potential kill shot,” said William, 74, hours later as he gathered with other relatives. “There were so many holes in that boy … you can’t even count them all.”

Melissa Nold, the family’s attorney, tried. It appeared to her that there were roughly 25 wounds, including in his face, the center of his throat, his chest and arms, she said. One ear was blown halfway off. Nold, a civil rights lawyer who has long represented families of police violence and who previously worked in a coroner’s office, said she had never in her entire career seen a more horrifying sight.

After seeing the body, William thought about his earliest memories of his nephew, changing his diapers as a baby 20 years ago. It was painful to think about how many obstacles Willie had overcome since then – only to have the people who were supposed to be public servants ending his life and destroying his body at a fast-food restaurant.

Facebook Twitter Pinterest Levonte Cole, AKA Pay Me, one of Willie McCoy’s cousins: ‘It hits us different every day.’ Photograph: Talia Herman/The Guardian

‘Music was his golden ticket’

Willie had a plan. Music would be his avenue to a better life – a “cliche from the bottom to the top” story, said one of his collaborators, a rapper known as SauceKing Ash.

“Financially, physically, mentally, he invested a lot into it,” he said. “When we were stagnant on our music or being lazy or slacking off, he would come get us and light the fire under our ass to get us going and get back to the studio.”

Willie survived a difficult childhood, losing his father when he was eight years old and then losing his mother just a few years later, both due to cancer. He subsequently grew up in between households and different cities, spending time in Vallejo, Oakland and Sacramento, and at one point living in group homes.

He was drawn to music at a young age, and in recent years began releasing tracks and music videos at a rapid pace, growing a sizable following on YouTube and collaborating with artists throughout the Bay Area and in other cities such as Detroit.

Some of his lyrics were earnest meditations about staying grounded in the face of adversity. In a song called How My Life Go, he said: “Seen a whole lot, had to forget about the past … It’s not that easy growing up without a dad / If I can keep my head up, then I won’t feel mad / They tryna bring me down, but I never get sad.”

“He was real. When you real, it touches people,” said Lawrence Clark, a local recording artist known as Pimp Style, who has long known Willie and his family. “They took a king.”

Multiple collaborators said Willie’s intense work ethic made him stand out.

“Music was his golden ticket. He took it very seriously,” said De Lon Adams, a 40-year-old Vallejo producer known as Fasethanation, who started recording Willie’s music in 2017. Willie would read up about the music business and talked to Adams about how to expand his fanbase and promote his work: “He was on a path to be a small business owner. He had already found success, and he was going to utilize his success for him and his homies.”

Seen a whole lot, had to forget about the past. It’s not that easy growing up without a dad Willie McCoy, How My Life Go

A constant theme in his music was “brotherhood and unity”, said BooBooMane. “What you want for yourself is what you want for your brother … sticking together, having each other’s back.”

Kori McCoy, one of Willie’s older brothers, said Willie displayed this rare kind of sweetness when he was a little boy that remained a constant his whole life: “He never left without telling me he loved me.”

Willie, who had FBG tattooed on his arm, also rapped about the criminal justice system, including one song last year inspired by his own arrest, where he talked about being guilty until proven innocent. (A spokesman for the district attorney said charges against him were dropped a month after they were filed.)

Another cousin of Willie, who goes by the rapper name TTG Dree, said it was natural for Willie and others to rap about law enforcement mistreating them: “People don’t hear us out. That’s the only way … of expressing ourselves.”

The 23-year-old added: “Police hate us. And they hated him.”

David, Willie’s older cousin, broke down thinking about everything Willie would have accomplished had police not cut his life short: “My whole family was robbed by six officers who felt that their life was in danger from a man asleep – a young black man with a whole bunch of potential.”

Facebook Twitter Pinterest Damariee Cole, AKA BooBooMane: ‘The music was about the hardships he overcame.’ Photograph: Talia Herman/The Guardian

‘Am I next?’

Vallejo police officials have repeatedly ignored the Guardian’s questions in the weeks since Willie’s death, declining to provide even basic details on the status of the investigation. In response to one local newspaper’s public records request, the department did recently release the name of the six officers who fired into Willie’s car: Ryan McMahon, Collin Eaton, Bryan Glick, Jordon Patzer, Anthony Romero-Cano and Mark Thompson.

McMahon killed an unarmed man last year and is currently facing a wrongful death lawsuit as a result. (The city denies he used excessive force.) Thompson was also previously named in a police brutality lawsuit, which was later settled. Neither officer could be reached for comment and the department did not respond to questions about their cases.

The fact that two of the officers who shot at Willie have past allegations of brutality on their records was of little surprise to local civil rights lawyers and other longtime Vallejo residents. The troubled police department has faced a wave of litigation over the years and was home to one officer who killed three men in a five-month period – and was subsequently promoted.

Families of those killed by Vallejo officers stood side by side at an emotional rally on Thursday, describing their “daily hell” of grief and their anger toward a “rotten” police agency that has acted like a “military occupying force”.

For some of Willie’s peers and relatives, their fear of police has escalated since his death. One said he felt anxious standing on the street for too long for fear that police might bother him. Others were reluctant to give their names due to concerns about police retaliation.

BooBooMane and SauceKing Ash said when they were once napping in a car, police approached them with guns drawn, which made the circumstances of Willie’s death all the more terrifying.

“I’ve been fearful all of my life … and wondering, am I next?” said BooBooMane.

Months earlier, Willie and his friends were more optimistic about their music than they had ever been. In a video David took on his phone of him, Willie and the other rappers hanging out in a studio, the young men appear giddy and hyped up as they talk about their recent successes, their videos getting thousands of views and kids recognizing them on the street.

“We gonna make it somewhere with this shit!” one of them says.

At one point, Willie takes a mic and talks about the struggles that tied them together: “Came from a whole lot of bad environments … but at the end of the day, all I’m saying is, this is fam right here … this is who we gonna be rocking with.” He holds up his FBG necklace with pride.

The video captures David appreciating the moment and the collaboration between all the young artists, saying: “Man, everything is right.”