The man arrested over the shooting and stabbing murder of British parliamentarian Jo Cox had ties to a neo-Nazi group in the United States, and had bought guides on assembling homemade guns and explosives, according to a US-based civil rights watchdog that tracks hate groups.
The Southern Poverty Law Center (SPLC) published records showing that Thomas Mair, 52, who allegedly shot and stabbed Cox multiple times Thursday, was a "longtime supporter of the National Alliance" (NA), once known as the US's premier neo-Nazi organization.
Mair reportedly spent more than $620 on books and literature from NA, including guides titled "Improvised Munitions Handbook," "Chemistry of Powder & Explosives," and "Incendiaries," according to receipts published by SPLC.
The receipts also showed Mair purchased a copy of Ich Kampfe — German for "I do battle" or "I struggle," and an obvious reference to Adolf Hilter's Mein Kampf —a handbook issued to new enrollees in the Nazi party in the early 1940s.
Mair also subscribed to S. A. Patriot, a South African magazine published by pro-apartheid group White Rhino Club, The Daily Telegraph reported.
Related: British Labour politician Jo Cox killed in shooting near Leeds
Cox, a 41-year-old lawmaker for the opposition Labour Party and a vocal advocate of Britain's European Union membership, died of her injuries on Thursday afternoon. She was attacked while preparing to meet constituents in Birstall near Leeds in northern England.
Media reports, citing witnesses, said the attacker had shouted out "Britain first", which is the name of a right-wing nationalist group that describes itself on its website as "a patriotic political party and street defence organisation".
Police said a 77-year-old man was also assaulted in the incident and suffered injuries that were not life-threatening.
Cox's death has caused deep shock across Britain and the suspension of campaigning for next week's referendum on the country's EU membership. The deputy leader of Britain First, Jayda Fransen, distanced the group from the attack, which she described as "absolutely disgusting". Leader Paul Golding also promptly condemned the attack.
One witness said a man pulled an old or makeshift gun from a bag and fired twice. "I saw a lady on the floor like on the beach with her arms straight and her knees up and blood all over the face," Hichem Ben-Abdallah told reporters. "She wasn't making any noise, but clearly she was in agony."
The lawmaker's husband Brendan said: "She would have wanted two things above all else to happen now: one, that our precious children are bathed in love and two, that we all unite to fight against the hatred that killed her."
The rival referendum campaign groups, Remain and Leave, said they were suspending activities on Friday. Prime Minister David Cameron said he would pull out of a planned rally in Gibraltar, the British territory on the southern coast of Spain.
Cameron said the killing of the mother-of-two, who had worked on US President Barack Obama's 2008 election campaign, was a tragedy.
"We have lost a great star," the Conservative prime minister said. "She was a great campaigning MP with huge compassion, with a big heart. It is dreadful, dreadful news."
It was not immediately clear what the impact would be on the June 23 referendum, which has polarized the nation into pro- and anti-EU camps. But some analysts speculated it could boost the pro-EU "Remain" campaign, which in recent days has fallen behind the "Leave" camp in opinion polls.
Gun ownership is highly restricted in Britain, and attacks of any nature on public figures are rare. The last British lawmaker to have been killed in an attack was Ian Gow, who died after a bomb planted by the Irish Republican Army (IRA) exploded under his car at his home in southern England in 1990.