The 22-year-old, from Washington, Utah, was charged with aggravated murder, weapon, and obstruction of justice offences ahead of a court appearance later on Tuesday.
Prosecutors said they would seek the death penalty and that Robinson's DNA was found on the trigger of the alleged murder weapon.
A note was also found under his keyboard which said: "I had the opportunity to take out Charlie Kirk and I'm going to take it," according to a charging document from prosecutors.
It is also alleged that the suspect ordered his roommate to delete "incriminating texts" about the killing and to stay silent if questioned by police.
When his roommate texted to ask if he was the "one who did it", Robinson replied: "I am, I'm sorry," prosecutors allege.
Robinson is said to have written in another text: "I had enough of his hatred. Some hate can't be negotiated out."
He also allegedly wrote he had been planning the shooting for just over a week.
Kirk, 31, was killed at one of his rallies at Utah Valley University last Wednesday.
The political activist, a close ally of US President Donald Trump, died after being shot in the neck with a bullet.
County attorney Jeff Gray said "aggravating factors" in the killing included that the "defendant is believed to have targeted Charlie Kirk based on his political expression and did so knowing children were present and would witness the homicide".
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The obstruction of justice charges relate to allegations that Robinson disposed of the weapon used in the killing, along with clothing he is said to have worn at the time.
Robinson has been held without bail since his arrest.
Investigators have spoken to Robinson's relatives and have carried out a search at his family home, 240 miles (385km) southwest of where the shooting took place.
Mr Gray said Robinson had accused Kirk of "spreading hate" during a conversation with his father. He also allegedly described the university as a "stupid venue" for the influencer to hold an event.
After the shooting, the county attorney said the suspect confessed to his parents after they confronted him, telling them he shot Kirk because "there is too much evil in the guy".
Robinson's mother told police that her son had become more political and had "started to lean more to the left" in the past year or so, Mr Gray said.
He added that the 22-year-old had become more "pro-gay and trans-rights oriented", according to his parents.
His mother said he had started to date his roommate, who was "transitioning genders", prompting "discussions" with his father who had very different political views.
Robinson allegedly wrote in another message to his roommate that "since Trump got into office [my father] has been pretty diehard Maga".
Redford, who was also the founder of the Sundance Film Festival, the largest independent film festival in the US, died on Tuesday morning.
In a statement, his representative said he was "surrounded by those he loved", at home in "the place he loved" in the mountains of Utah. "He will be missed greatly," she added.
Born Charles Robert Redford Jr in Santa Monica, California, in 1936, he attended college on a baseball scholarship but later went on to study at the American Academy of Dramatic Arts.
He debuted on Broadway in the late 1950s before moving into television, in shows such as The Twilight Zone, Alfred Hitchcock Presents and The Untouchables.
Rising to stardom in the 1960s, Redford became a go-to leading man in Hollywood and a huge star of the following decade, leading films including The Candidate, All the President's Men and The Way We Were.
He worked hard to transcend being typecast for his good looks, through his political advocacy and a willingness to take on unglamorous roles.
In the 1990s and 2000s, his film credits included Indecent Proposal, The Last Castle and Spy Game, and he also worked actively as a filmmaker - helming movies including A River Runs Through It and The Legend Of Bagger Vance. In 1998, he both starred in and directed The Horse Whisperer.
But he was best known for his role as wily outlaw the Sundance Kid, opposite Paul Newman's Butch Cassidy in the 1969 film. The pair became a famous screen partnership, starring opposite each other again in The Sting a few years later, and good friends.
As well as his starring roles, Redford was also an activist and an accomplished filmmaker - winning the Oscar for best director for Ordinary People in 1981. He had four Academy Award nominations in total - the first for acting for his performance in The Sting - as well as an honorary prize in 2002.
In a career spanning seven decades, he also received three Golden Globe Awards, including the Cecil B DeMille lifetime achievement honor in 1994.
In his later years, Redford took on a challenging role in All Is Lost, a 2013 survival story that featured virtually no other characters and barely any dialogue. His performance earned a standing ovation after the film was screened at the Cannes Film Festival.
In 2018, he received critical acclaim again in what he called his farewell movie, The Old Man And The Gun.
His legacy lives on in the Sundance Film Festival, which grew into a cornerstone of the film industry and provided a launching pad for filmmakers including Quentin Tarantino, Paul Thomas Anderson, Steven Soderbergh, Gina Prince-Bythewood and Darren Aronofsky.
And in 2016, former President Barack Obama awarded him the presidential medal of freedom - considered the US government's highest civilian honour - saying at the time that Americans "admire Bob not just for his remarkable acting, but for having figured out what to do next".
Robert Redford leaves behind his wife Sibylle Szaggars and two daughters - Shauna, a painter, and Amy, an actress and director.
He was previously married to Lola Van Wagenen. One of their children, Scott, died at the age of two months from sudden infant death syndrome. Another, James, died of cancer in 2020.
'One of the lions has passed'
Tributes have been shared across social media following the announcement of Redford's death.
Meryl Streep, who starred in Out Of Africa and Lions For Lambs opposite Redford, said: "One of the lions has passed. Rest in peace my lovely friend."
Filmmaker Ron Howard, known for Apollo 13 and A Beautiful Mind, described Redford as "a tremendously influential cultural figure for the creative choices" he made as an actor, producer and director, and said Sundance had been a "gamechanger".
Marlee Matlin, star of the Oscar-winning CODA, said the film "came to the attention of everyone" because of the Sundance Festival.
"Sundance happened because of Robert Redford. A genius has passed," she said.
"He was part of a new and exciting Hollywood in the 70s and 80s," wrote author Stephen King. "Hard to believe he was 89."
Spencer Cox, the governor of Utah, wrote: "Decades ago, Robert Redford came to Utah and fell in love with this place.
"He cherished our landscapes and built a legacy that made Utah a home for storytelling and creativity.
"Through Sundance and his devotion to conservation, he shared Utah with the world. Today we honor his life, his vision, and his lasting contribution to our state."
In a statement, the Sundance Institute said: "We are deeply saddened by the loss of our founder and friend Robert Redford. Bob's vision of a space and a platform for independent voices launched a movement that, over four decades later, has inspired generations of artists and redefined cinema in the US and around the world.
"Beyond his enormous contributions to culture at large, we will miss his generosity, clarity of purpose, curiosity, rebellious spirit, and his love for the creative process. We are humbled to be among the stewards of his remarkable legacy, which will continue to guide the Institute in perpetuity."
The trio were joined by other royals at Westminster Cathedral for the requiem mass - a Catholic funeral - the first to be held for a member of the Royal Family in modern British history.
Katharine, Duchess of Kent, who became the oldest living member of the Royal Family on the death of Queen Elizabeth II in 2022, died at the age of 92 on 4 September.
It emerged earlier that the Queen had withdrawn from attending while she recovers from illness.
Buckingham Palace said on Tuesday that Camilla, 78, is recovering from acute sinusitis, with the withdrawal raising questions over her attendance for US President Donald Trump's state visit, which begins at Windsor on Wednesday.
That visit is being hosted by the King, but the Queen is understood to be hopeful she will recover in time to attend all royal elements of Mr Trump's trip, which includes a lavish state banquet.
A Buckingham Palace spokesperson said: "With great regret, Her Majesty the Queen has withdrawn from attendance at this afternoon's requiem mass for the Duchess of Kent as she is recovering from acute sinusitis."
The Duke of Kent was informed and was said to fully understand the decision, wishing her a speedy recovery.
The Queen had travelled down from Scotland this morning and is currently travelling to Windsor, where she will rest.
"Her thoughts and prayers will be with the Duke of Kent and all the family," the spokesperson added.
During the service, Pope Leo XIV paid a personal tribute to the Duchess of Kent, praising her "legacy of Christian goodness" in a message delivered during her funeral.
In words read out by Archbishop Miguel Maury Buendia, the pontiff highlighted her "dedication to official duties".
Prince Andrew and Sarah, Duchess of York, were seen approaching Westminster Cathedral for the service.
Former Formula 1 world champion Sir Jackie Stewart and actresses Rula Lenska and Dame Maureen Lipman were also among the mourners.
New York state judge Gregory Carro said there was no evidence that the killing of UnitedHealthcare (UHC) chief executive Brian Thompson amounted to a terrorist act.
However, he upheld prosecutors' demand that the 27-year-old face second-degree murder charges - meaning there was malicious intent behind the killing but it was not premeditated.
Mangione has previously pleaded not guilty to multiple counts, including murder as an act of terrorism, over the killing of Mr Thompson.
The UHC boss was shot dead as he arrived for an investor conference at the New York Hilton Midtown on 4 December 2024.
Mangione was arrested five days later after he was spotted at a McDonald's in Altoona, Pennsylvania, about 230 miles west of New York City.
In his written decision, the judge said that although the killing was not a case of ordinary street crime, it did not meet the threshold for terrorism under New York law.
"While the defendant was clearly expressing an animus toward UHC, and the healthcare industry generally, it does not follow that his goal was to 'intimidate and coerce a civilian population', and indeed, there was no evidence presented of such a goal," Judge Carro wrote.
The terrorism charges carried a maximum sentence of life in prison.
However, as well as the case in New York state, Mangione is also facing separate federal murder charges, which could see him being sentenced to death if convicted. The federal case does not involve terrorism allegations.
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The suspect's lawyers argued that the parallel prosecutions had created a "legal quagmire" and amounted to double jeopardy, although Judge Carro rejected the claim.
Further pretrial hearings, for both the federal and state cases, will be held in December.
US Attorney General Pam Bondi said in April that she had asked federal prosecutors to seek the death penalty for "an act of political violence" and a "premeditated, cold-blooded assassination that shocked America".
The Manhattan district attorney's office quoted extensively from Mangione's alleged handwritten diary in a court filing seeking to uphold his state murder charges.
In the writings, prosecutors said, Mangione wrote about rebelling against "the deadly, greed-fuelled health insurance cartel" and said killing an industry executive "conveys a greedy bastard that had it coming".
They added that the writings "convey one clear message: that the murder of Brian Thompson was intended to bring about revolutionary change to the healthcare industry".
The report claims "it is clear that there is an intent to destroy the Palestinians in Gaza" and says Israel's actions meet the criteria set down for defining a genocide.
It is the first time that such an explosive allegation has been made publicly by a UN body, and is likely to be greeted with fury by the Israeli government.
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Israel's Foreign Ministry said it "categorically rejects this distorted and false report" and called for the commission to be abolished.
"Three individuals serving as Hamas proxies, notorious for their openly antisemitic positions - and whose horrific statements about Jews have been condemned worldwide - released today another fake 'report' about Gaza," it said in a statement.
"The report relies entirely on Hamas falsehoods, laundered and repeated by others. These fabrications have already been thoroughly debunked."
The accusation of genocide is made by the UN Independent International Commission of Inquiry on the Occupied Palestinian Territory.
The commission, which has been studying the conduct of Israel since the Hamas attacks of 7 October 2023, has concluded that Israel has committed four of the five acts laid out in the Genocide Convention.
It alleges Israel has been killing Palestinians or forcing them to live in inhumane conditions that led to death; causing serious bodily or mental harm, including through torture, displacement and sexual crime; deliberately imposing inhumane conditions, and fourthly, imposing measures intending to prevent births.
This final claim is linked to an attack on the Al-Basma IVF clinic, which the commission claims destroyed around 4,000 embryos and a further 1,000 sperm samples.
The report claims Israel has "flagrantly" ignored "numerous warnings" over the humanitarian crisis in Gaza and has set out to "destroy the healthcare system in Gaza".
It also alleges that Israeli military personnel have carried out sexual and gender-based violence, including "rape and sexualised torture", as part of "a pattern of collective punishment", and accuses Israeli forces of deliberately targeting some children "with the intention to kill them".
Although other UN bodies and personnel have previously linked Israel's actions with allegations of genocide, this is the first time that any UN body has claimed to have made a definitive judgment.
"The responsibility for these atrocity crimes lies with the Israeli authorities at the highest echelons," said Navi Pillay, the chair of the commission.
Within the report, it concludes that "Israeli President Isaac Herzog, Prime Minister Benjamin Netanyahu and then Defence Minister Yoav Gallant, have incited the commission of genocide".
Nearly 65,000 people are now believed to have died, according to figures collated by Gaza's health ministry. It does not distinguish between civilians and combatants in its count.
The commission claims that a majority of these are women, children and elderly people.
The commission says it is now looking at further evidence against other individuals accused of inciting genocide.
Last year, the International Criminal Court (ICC) issued arrest warrants against both Mr Netanyahu and Mr Gallant for allegedly committing the war crime of using starvation as a method of warfare and also for war crimes during the Gaza conflict.
Mr Netanyahu described the warrants as "antisemitic", while a sense of outrage echoed across much of the political spectrum in Israel.
Then US President Joe Biden called the warrants "outrageous"; his successor, Donald Trump, issued an executive order to introduce sanctions against personnel from the ICC, while inviting Netanyahu to the White House.
It is hard to believe that either Israel or the US will be any more accepting of this report. Israel has long claimed that the UN is biased against it and is more liable to criticise Israel than any other nation.
The US, which offered a rare, if mild, rebuke to Mr Netanyahu after he launched an attack on Hamas officials in Qatar last week, has since sent Secretary of State Marco Rubio to Jerusalem as a sign of solidarity.
The commission has asked for nations to stop supplying Israel with weapons and says states have a "legal obligation" to do everything within their power "to stop the genocide in Gaza".
It also calls on Israel to immediately allow "unhindered" access for internationally recognised aid agencies, including the UN.
It wants the Gaza Humanitarian Foundation (GHF), set up earlier this year by Israel with American help, in order to distribute aid, to be shut down.
Hundreds of people have been killed around GHF sites, while a separate UN-backed body has said that parts of Gaza have been designated as suffering from famine.
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Israel denies this - a senior military leader told me that "it is a pure, total lie - there is enough food for everyone". It claims that the UN relied on faulty data and Hamas propaganda.
This latest UN report is likely to be met with similar claims.
Earlier this month, the International Association of Genocide Scholars passed a resolution stating that Israel's conduct passed the threshold of committing genocide.
However, a report from the British government said it had "not concluded" that Israel intended to "destroy in whole or in part a national, ethnic, racial or religious group".