When the ambulances and trucks and cars started streaming into hospitals with their human cargo, the emergency room doctors set up a system.

The walking wounded got green tags, the seriously injured got yellow and those close to death got red. All night it went: a bloodied arrival, a swift assessment, a tag – green, yellow, red, colour-coding for the deadliest mass shooting in modern United States history.

Those who could not be saved were set aside in separate rooms to be made as comfortable as possible until they died. The red streaks staining the corridors and entry bays shocked even the paramedics. There was so much.

By the time the sky paled over Las Vegas on Monday, 59 people were dead, including the shooter, 489 were injured, stories of heroism and survival were emerging and a week-long macabre ritual was in motion, a choreography of atrocity in which everyone knew their role.

Donald Trump for once hewed to convention and played comforter-in-chief, hailing the bravery of first responders and patients he met at the University Medical Center. “America is truly a nation in mourning. When the worst of humanity strikes, and strike it did, the best of humanity responds.”

Congress reprised gun control arguments honed and polished from previous mass shootings. The media staked out hospitals and stood in front of yellow crime scene tape. Conspiracy theory peddlers claimed it was all fake.

The National Rifle Association hunkered down, waiting for the storm to abate, and issued a call on Thursday to regulate bump stocks, devices which turn semi-automatic rifles into rapid-fire weapons. If everything went the NRA’s way, this latest massacre would be the 11-minute rampage that shook America – and effected just a marginal tweak to gun laws.

The only thing missing was motive.

Volunteers build a community healing garden in Las Vegas. Photograph: Robyn Beck/AFP/Getty Images

Why did Stephen Paddock, a 64-year-old accountant-turned professional gambler, stockpile an arsenal in his room on the 32nd floor of the Mandalay Bay hotel and rain havoc on the outdoor country music festival below before taking his own life? The enigma gaped like the hole he smashed in the hotel window, a black cavity in a tower of gold-tinted glass.

It emerged that the previous weekend, Paddock had reserved a room via Airbnb at the Ogden luxury apartment complex, which overlooked the site of the Life is Beautiful festival, featuring acts such as Gorillaz and Lorde.

“Was he doing pre-surveillance? We don’t know yet,” Sheriff Joseph Lombardo told a press conference on Wednesday. He speculated that Paddock had help, earning a veiled rebuke from Aaron Rouse, who runs the FBI’s Las Vegas division. “Theories are great and everyone can have a theory. But I need to deal with facts.”

Paddock’s nomadic lifestyle shuttling between various homes and casinos left few clues – virtually no close friends, social media presence or engagement with the wider world. His girlfriend, Marilou Danley, 62, returned from the Philippines professing horror and mystification. “It never occurred to me in any way whatsoever that he was planning violence against anyone,” she said in a statement read out by her lawyer.

No known suicide note, no obvious grudge or ideological agenda. “We look for actual indicators of affiliation, of motive, of intent, and so far we’re not there,” said the FBI deputy director, Andrew McCabe. “We don’t have those sort of indicators.”

So Paddock remained a grey figure. Except for the fact he was white, and not Muslim. Thus the week passed without headlines declaring this the worst domestic terrorism event since 9/11, without Trump doubling down on the travel ban or weighing options against the killer’s country of origin.

“What happens when the country of origin is us?” Thomas Friedman asked in the New York Times.

A makeshift memorial is pictured in the middle of Las Vegas Boulevard following the mass shooting. Photograph: Chris Wattie/Reuters

This is what happened on Sunday night. Paddock was in room 32135 of the Mandalay Bay with more than 10 suitcases, 23 guns, stacks of ammunition, bump stocks and a hammer, apparently to break the window.

At approximately 10.08pm he opened fire on the Route 91 Harvest country music festival, 400 yards away across the highway, just as Jason Aldean’s band, the headline act, was finishing a guitar riff. Bullets tore into the 22,000-strong crowd.

“We heard that initial popping sound. Of course, we thought it was fireworks,” said Krista Metz, 45, from San Diego. “You could just see [Aldean’s] face. He just stopped singing. He ran off the stage and the lights went out. Now you could hear the popping wasn’t fireworks.”

Metz and her cousin ran to a barrier and lay on the ground but got trampled so resumed running. “We ended up coming to a big fence with spikes on the top. Somehow adrenaline got us up and over that. We must have fallen down three or four times. We had random people pick us up and help us keep running. I feel like we were so lucky. We were running and we literally thought we were going to die and get shot in the back of the head.”

Heroism abounded.

Mike McGarry, a financial planner from Philadelphia, lay atop people seeking cover. “I’m 53, they’re in their 20s. I lived a decent life so far, I’d rather them live longer than me,” he told KYW-TV.

Jonathan Smith, a 30-year-old copy machine repairman from California, herded dozens to relative safety in a disabled parking area until he was shot. He survived but the bullet may remain lodged in his neck for the rest of his life.

Nick Campbell, a 16-year-old from Henderson, was haemorrhaging blood from his shoulder when a stranger – “probably in his 20s, tan, possibly Hawaiian and buff” – used backpack straps to staunch the bleeding and carried him to safety.

Amber Ratto, 26, a paramedic, ferried a wounded husband and wife to hospital in her ambulance then, splattered in blood, drove right back to the killing zone. “I turned off the lights in the back of the ambulance to not be targets.”

Emergency room teams worked amid controlled chaos. Some patients walked and staggered, moaning and wailing; others lay on stretchers, motionless and silent. Some had multiple wounds to the head, face, chest, body, arms and hands, others had just single wounds or abrasions, testament to the indiscriminate fire.

“Blood on the ground in the car park – trails of blood about 20ft from the entrance,” said Robert Smith, a cardiovascular technician at the University Medical Center. “You couldn’t think about your own world, your own problems. You had to focus on the patients to save as many lives as possible.”

The dead included Cameron Robinson, 28, a city of Las Vegas employee who ran the office potluck and Christmas party; Tara Smith, 34, a Canadian model with two young children; Carrie Barnette, 34, a Disneyland culinary worker “always with a smile”; Sonny Melton, 29, a nurse from Tennessee who shielded his wife; Sandy Casey, 35, a middle school teacher engaged to be married.

Collages of the smiling faces of lives erased formed part of the media ritual. So too the rolling news, with anchors relocating to the stricken city.

“What cable news does best now begins, and will continue for the next seventy-two hours: the slow and luxurious licking of tears from the faces of the bereaved,” wrote Stephen King. That was in Guns, a 2013 essay published after the Sandy Hook massacre, but the novelist was describing, as he saw it, institutionalised atrocity voyeurism.

There was certainly a weary familiarity to the scenes of grief, but this time they were in America’s playground, Sin City.

Would what happened in Vegas stay in Vegas? The slogan itself was under question, with R&R Partners, the advertising agency that developed it, listening “very keenly” to potential alternatives.

‘Our guns are the only thing we have to protect us from our government,’ said Mark Rumpler. Photograph: Rory Carroll/The Guardian

Ever so slightly, the Mojave desert heat seemed to melt the frozen tundra of gun control policy, with congressional Republicans appearing to endorse the NRA’s rare concession in urging “additional regulations” on bump stocks. However, the group also urged further relaxation of laws permitting Americans to carry concealed firearms.

Caleb Keeter, a guitarist with a band that came under fire, said the trauma had converted him to gun control. “Enough is enough.”

Others, however, saw no reason for change.

“In countries with gun control, they mow you down with cars,” said Joseph Bernardo, 57, a recreational vehicle salesman, as he lay flowers at a makeshift memorial by the Las Vegas sign.

“Hate finds a way,” said Angela, another Las Vegas resident, who brought red roses. “They’ll stab you with a butter knife if that’s all they have.”

Mark Rumpler, 58, an Elvis impersonator in a white jumpsuit who was waiting to perform a wedding at the sign, said guns deterred tyranny. “Our guns are the only thing we have to protect us from our government.”

One small part of Las Vegas did change: workers turned a half-acre plot of vacant city-owned land at Charleston and Casino Center boulevards into a “healing garden”, with 58 trees to honour each of those murdered. It was due to open on Friday night. A patch of green to “create something beautiful out of something horrific”, said a city news release.

Additional reporting by Sam Levin in San Francisco