The killing appeared so well-planned that at first glance many assumed it was a professional hit.

The gunman who shot dead Brian Thompson, head of one of the US’s largest health insurance companies, on a New York street before dawn lay in wait with a weapon fitted with a silencer, kept his cool as his gun jammed and made a nimble escape after ensuring that his victim had been fatally struck.

However, within hours, an intense police manhunt turned up a trail of clues and possible mistakes, suggesting that while the killer had taken care to cover his tracks, he also made amateurish missteps that may yet lead to his identification and capture.

But millions of Americans were less interested in the mechanics of what New York’s new police commissioner, Jessica Tisch, called “a premeditated, pre-planned, targeted attack” than the possible motive. Despite the fact the killer’s motive remains completely unknown, the death of UnitedHealthcare’s CEO unleashed an eruption of anger from people mistreated, or untreated, by the US’s rapacious medical industry and even a grim schadenfreude from some at Thompson’s death.

Hundreds of thousands of Americans are driven into bankruptcy every year by medical debts, with many of them losing their homes. Thousands die because insurance companies find reasons not to pay for treatment, including UnitedHealthcare, which denies about one-third of claims.

Anthony Zenkus, a lecturer at the Columbia School of Social Work, spoke for many in a post on X.

“Today, we mourn the death of United Healthcare CEO Brian Thompson, gunned down…. wait, I’m sorry – today we mourn the deaths of the 68,000 Americans who needlessly die each year so that insurance company execs like Brian Thompson can become multimillionaires,” he wrote.

The revelation that shell casings at the scene were marked with the words “deny” and “defend” and “depose” added weight to speculation that the killer had had a vendetta against UnitedHealthcare, which earned $280bn in revenue last year insuring about 50 million people in the US. Two of the words are used by the industry in policy documents and were included in the title of a 2010 book, Delay, Deny, Defend: Why Insurance Companies Don’t Pay Claims and What You Can Do About It.

Thompson was in New York from UnitedHealthcare’s headquarters in Minnesota for an investor conference. The 50-year-old father of two had been appointed the company’s CEO in 2021 and was paid $10m last year after overseeing a sharp rise in profits to $16bn that some critics said came from using artificial intelligence to routinely reject claims.

His killer appears to have been well-informed about Thompson’s movements. The assailant apparently knew when his victim was likely to arrive at the New York Hilton Midtown hotel close to Central Park and which entrance he would use.

Surveillance footage captured the gunman outside the hotel at about 6.30am wearing a dark hooded jacket and a black mask and carrying a grey backpack as he made a phone call. Thompson is seen in a blue suit walking up to a hotel door about 15 minutes later, more than two hours before the shareholder meeting was to begin.

The gunman stepped from behind a car and raised a pistol. He fired at least twice, hitting his victim in the calf and the back. Thompson briefly continued walking before turning to face his killer and then collapsing.

The police described the attacker as “proficient in firearms” as video showed him swiftly clearing the firing mechanism of his gun when it jammed and unleashing another bullet. The assailant then walked up to Thompson as he lay slumped against a wall and raised his gun but apparently did not fire again.

The killer then crossed the road and ran into an alleyway, which took him past the Ziegfeld Ballroom and onto West 55th Street. There he jumped onto an electric bike, turned north onto 6th Avenue and headed into Central Park, where he dumped the backpack found by officers on Friday.

The police said that after he left the park, the suspect took a cab and then a bus out of the city but have not publicly identified where it was headed.

The police rapidly uncovered a series of potential clues including a cellphone in the passageway the gunman fled along and video footage of the killer in a Starbucks close to the hotel shortly before the shooting. Detectives attempting to trace the origin of the pistol were following a lead with a Connecticut gun dealer who sold a weapon resembling the one used in the killing.

But there were also red herrings. Much was made of initial police claims that the killer had used an electric Citi Bike, which require a credit or debit card and a phone app to rent, and are fitted with GPS trackers. That was expected to provide vital clues. The next day, the police backed off that claim and instead focussed on whether the killer had used an unmarked electric bike that he either positioned for a getaway or stole from off the street as he fled.

By Thursday, investigators had put together an outline of the gunman’s movements before the shooting. They concluded he had arrived in New York about 10 days before the killing on a bus that had travelled from Atlanta, although it is not yet known where he boarded. He then stayed at a hostel on Manhattan’s Upper West Side, using a fake New Jersey ID to check in and sharing a room with two strangers for at least part of the time.

One of the most significant finds was of surveillance footage of the gunman at the hostel after he pulled his mask down, reportedly in a brief flirtation with a female employee, leading to the possibility he will be recognised by someone who knows him or identified by facial recognition technology. The man, who appears to be relatively young, is seen smiling in one picture and looking more serious in another.

On Friday, officials said investigators had also found DNA evidence that has been sent for testing.

There was less information about the killer’s motives but that did not stop a flood of conjecture, much of it premised on bitter experience at the hands of the medical insurance industry.

Thompson was separated from his wife, Paulette, who fueled the speculation that he had been shot by someone with a grudge against UnitedHealthcare in her initial reaction to NBC News. “There had been some threats. Basically, I don’t know, a lack of coverage? I don’t know details. I just know that he said there were some people that had been threatening him,” she said.

That there was plenty of public anger at UnitedHealthcare was not a secret.

Earlier this year, protesters from across the country rallied outside the company’s headquarters in Minnesota over its refusal to pay about one-third of claims, according to research by ValuePenguin, more than any other health insurer.

Regulators and politicians have accused the company of boosting profits by systematically rejecting care to which people are entitled under their policies or of refusing to meet the full cost and leaving patients in debt.

In October, a US Senate committee released a report cataloging how UnitedHealthcare and other companies deny patients care after they have been discharged from hospital following acute operations, even when doctors say it is necessary for a full recovery. The report said that the denials are principally made to drive up profits.

The day before Thompson was killed, the American Society of Anesthesiologists issued a statement condemning another health insurance company, Anthem Blue Cross Blue Shield, for imposing a limit on the amount of time for which it was prepared to pay for patients having surgery to receive anaesthesia. The company reversed its position after the shooting.

But Thompson’s death unleashed something more visceral from people who feel helpless in the face of giant medical corporations with the power of life or death.

A woman on TikTok relayed her own experience at the hands of UnitedHealthcare when she was nine months pregnant and at a hospital with a one-year-old baby who had just been diagnosed with “a giant brain tumour”. The woman said the child required emergency surgery at a nearby hospital in a neighbouring state.

“We sat in the hospital for three days because UnitedHealthcare refused to approve the transfer via ambulance from the hospital where we live to another state. And at that point, I was ready to just get in my car and take her there myself. But UnitedHealthcare told us if we left the hospital by our own will, and it wasn’t via ambulance, they were not going to cover her at the next hospital we went to,” she said.

“I vividly remember being on the phone with UnitedHealthcare for days and days, nine months pregnant, about to give birth alone, while my other baby was sitting in a hospital room. And, again, this isn’t to condone violence whatsoever. All I’m saying is that I do not doubt for a second what the motive of that suspect was.”

Others quoted Woody Guthrie: “Some rob you with a six-gun, some with a fountain pen.”

The backlash came not only from patients but doctors who recounted UnitedHealth refusing to pay for a child with cancer to receive medicines for the side effects of chemotherapy and questioning the necessity of lifesaving care. The outpouring of anger from within the medical profession at Thompson as representative of the greed of the insurance industry at the cost of lives caused Reddit moderators to delete a thread for the medical community, according to the Daily Beast.

The health insurance industry is only one part of a medical system that the Princeton economists Anne Case and Angus Deaton, who won the 2015 Nobel prize for economics, have described as a “Sheriff of Nottingham redistribution” in the fleecing of ordinary Americans to give to rich corporations.

The pair published a study four years ago, Deaths of Despair and the Future of Capitalism, that concluded the US health industry is killing staggering numbers of patients while making Americans poorer.

“The American healthcare system is a leading example of an institution that, under political protection, redistributes income upwards to hospitals, physicians, device-makers, and pharmaceutical companies while delivering among the worst health outcomes of any rich country,” the economists wrote.

As the medical industry has grown more rapacious, charging more for operations and prescription drugs, so insurance premiums have surged and patients been required to make ever larger out-of-pocket payments that can amount to thousands of dollars a year. Or they find their claims denied.

If the killer is caught, and his motive is as many Americans imagine it to be, his trial could prove to be yet another divide in an already fractured nation. Even if the killer was not motivated by that anger, the outpouring of public rage against the healthcare industry should serve as some kind of warning for its leaders.