The killing of a promising young British lawmaker who advocated passionately for refugees spawned a national reckoning Friday over a political culture that has turned increasingly intolerant in the final days of a bitter campaign to determine whether the country leaves the European Union.

The soul-searching spawned by the death of 41-year-old Jo Cox has the potential to reset the tone of the E.U. debate and could influence its outcome when the country votes Thursday.

Any overt campaigning has been put aside until Sunday as the nation continues to mourn Cox, who died Thursday afternoon after being stabbed and shot outside the library in this quiet northern English market town.

But revelations that the alleged perpetrator had long-standing affiliations with neo-Nazi and other far-right groups prompted a widespread demand Friday for an end to the divisive rhetoric that has marred the referendum campaign.

In a rare joint appearance, British Prime Minister David Cameron and Labour Party leader Jeremy Corbyn visited the makeshift memorial set up near the site where Cox was killed. Both called for a kinder and less poisonous brand of politics.

Witnesses told British media that the assailant appeared to have been waiting for Cox outside a library in the town of Birstall, where she had been meeting constituents. (TWP)

“Where we see hatred, where we find division, where we see intolerance, we must drive it out of our politics and out of our public life and out of our communities,” Cameron said.

Corbyn blamed the killing on “a well of hatred” and described it as “an attack on democracy.”

Much of the E.U. referendum campaign has been dominated by anxiety over immigration, with supporters of an exit arguing that Britain risks being overrun by newcomers if it does not leave the 28-member bloc and erect higher barriers to entry.

Police said Friday they are still investigating what led the killer to attack Cox. But witnesses at the scene reported that a man appeared to have been waiting for her outside the library, and that he shouted “Britain first!” during and after the assault. The man was arrested as Cox lay dying on the sidewalk.

Dee Collins, the temporary chief constable of the West Yorkshire Police, said in a statement Friday evening that possible links to right-wing extremism were a “priority line of enquiry” in the investigation. She said the alleged perpetrator’s mental health was also being examined.

Early on Saturday, police announced charges of murder against 52-year Thomas Mair, a longtime resident of Birstall.

The British media has reported that neighbors and family members have described Mair as quiet and seemingly apolitical.

But according to documents obtained by the Southern Poverty Law Center, a U.S.-based organization that tracks extremist groups, Mair was a longtime supporter of the National Alliance, a once-prominent white-supremacist group. In 1999, Mair bought a manual from the organization that included instructions on how to build a pistol, the center said.

Cox was shot with a weapon that witnesses described as either homemade or antique, though the BBC reported Friday that police did not think the weapon had been assembled by Mair.

In all, Mair sent $620 to the National Alliance’s publishing arm for titles including “Incendiaries,” “Chemistry of Powder and Explosives,” “Improvised Munitions Handbook” and “Ich Kampfe,” published by the World War II-era Nazi party, the law center said.

Various British media outlets also reported that Mair had subscribed to a South African magazine published by the White Rhino Club, a pro-apartheid group.

Nick Lowles, chief executive of the British-based anti-extremist group Hope Not Hate, said Mair had an affiliation with far-right groups that stretched back decades, although he was not a prominent player in any of them.

“It fits a pattern of far-right attacks. We’ve had a number of these lone wolves — men in their 50s who are on the periphery of these movements and who believe that the battle is coming,” he said. “On the one hand, they’re on their own. But they’ve also been inspired by a lot of the things they read.”

It remains unclear whether the attack had any links to debates over immigration ahead of the E.U. vote next Thursday, Lowles said. But he described the current atmosphere as “increasingly toxic.”

“That leads to increased prejudice. That leads to increased hate. And, at some stage, that leads to violence,” he said. “Whatever the outcome next week, the U.K. has become a much more intolerant and divided society. It’s going to take a long time to heal.”

On the day of the shooting, Nigel Farage, the leader of the anti-immigration U.K. Independence Party, unveiled a referendum campaign poster showing a massive line of migrants and refugees along with the slogan: “Breaking Point. We must break free from the E.U. and take control of our borders.”

Nicola Sturgeon, the first minister of Scotland, called the ad “disgusting.”

“When you shout ‘breaking point’ over and over again, you don’t get to be surprised when someone breaks,” said the Spectator magazine’s Alex Massie. “When you present politics as a matter of life and death, as a question of national survival, don’t be surprised if someone takes you at your word. You didn’t make them do it, no, but you didn’t do much to stop it, either.”

With flags flying at half-staff outside 10 Downing Street and Buckingham Palace, both sides in the E.U. referendum debate said they would hold off on any major campaign activity until Sunday. Recent polls have shown the campaign is effectively tied, with “out” perhaps holding a slight advantage.

Security will be a concern when campaigning resumes, a rarity in British politics. Collins, the police official, said authorities think the assault on Cox was “a single isolated attack.” But threats against members of Parliament have been rising in recent weeks.

Anna Turley, a Labour lawmaker, told the BBC that she and Cox talked often about the “increasing nature of hostility and aggression, particularly towards female [members of Parliament], particularly on social media.” Turley added, “We were all reviewing our security.”

But she insisted that “Jo would not have wanted us to be hidden and be behind walls.”

Before Cox won election to Parliament last year, the mother of two had a career in humanitarian work, including for the aid organization Oxfam. She was a strong advocate for an inclusive and multicultural Britain, and she pushed for the country to take in thousands of child refugees.

People who knew her — and those who did not — placed flowers at the foot of a statue in Birstall’s central square throughout the day Friday. Also left in tribute: heartfelt letters, poems and cards expressing sorrow and disbelief.

The visitors reflected the diversity of the community. White Britons, Eastern European immigrants and members of the area’s long-standing South Asian community gathered to pay respects.

“She was genuine, caring. A proper Yorkshire lass,” said Nazir Daud, 41. “She wasn’t one of those politicians who just tries to make her name. She genuinely worked hard for the community.”

Daud said Cox never failed to return his calls or text messages relaying concerns among worshipers at his mosque. He scrolled through a stream of text exchanges to find the last: a message from Cox wishing him a happy Ramadan.

“She stood for a multicultural vision of Britain,” he said. “She was always fighting for justice and equality.”

And that, Daud said, was also why she was killed.

Adam reported from London.