Police investigating the killing of British member of Parliament Jo Cox said Friday that the mental health and possible links to right-wing extremism of Thomas Mair, the man charged with her murder, are both important lines of inquiry for detectives.

Campaigning in Britain's European Union membership referendum and normal political life were suspended as the country absorbed the slaying with shock — and worry that the political fury unleashed by the EU campaign was somehow connected to the killing.

Temporary chief constable Dee Collins of West Yorkshire Police says counterterrorism detectives are helping with the investigation.

"We are aware of the speculation within the media in respect of the suspect's link to mental health services, and this is a clear line of inquiry which we are pursuing," she said. "We are also aware of the inference within the media of the suspect being linked to right-wing extremism, which is again a priority line of inquiry which will help us establish the motive for the attack on Jo."

Collins said the suspect, named locally as 52-year-old Thomas Mair, was examined and declared fit to be interviewed by detectives.

West Yorkshire police said on their website that Mair faces murder and other charges.

"We have now charged a man with murder, grievous bodily harm, possession of a firearm with intent to commit an indictable offence and possession of an offensive weapon," West Yorkshire Police Det. Supt. Nick Wallen said in a statement.

Mair is due to appear at Westminster Magistrates' Court on Saturday, Wallen said.

Update re death of Jo Cox, MP. Man charged with murder and other offences <a href="https://t.co/7AIMUpIvSb">https://t.co/7AIMUpIvSb</a> —@WestYorksPolice

Suspect supported 'violent neo-Nazi group'

Heidi C. Beirich of the Southern Poverty Law Center said Mair had been a supporter of the National Alliance, "the most dangerous and violent neo-Nazi group in the United States for decades."

The centre, an Alabama-based group that monitors hate groups, said it had obtained documents showing that Mair bought books and magazines from the National Alliance on three occasions in 1999 and 2003.

On its website, the centre published copies of receipts showing that in 1999 a Thomas Mair of West Yorkshire — the county where Cox and her suspected killer both lived — bought publications including Chemistry of Powder and Explosives and the Improvised Munitions Handbook. In 2003 he purchased a subscription to the group's magazine, Free Speech.

Thomas Mair (alleged killer of <a href="https://twitter.com/hashtag/JoCox?src=hash">#JoCox</a>) purchased handbook that details how to build a gun <a href="https://t.co/JHE1yTYBlr">https://t.co/JHE1yTYBlr</a> <a href="https://t.co/pJtsbghbpT">pic.twitter.com/pJtsbghbpT</a> —@splcenter

The address on the receipts corresponded to a house that was cordoned off by police tape and guarded by uniformed officers on Friday.

The National Alliance was founded by William Pierce, whose book The Turner Diaries has been called a grisly blueprint for a race war. Timothy McVeigh based the 1995 bombing of the Oklahoma City federal building, which killed 168 people, on a truck-bombing described in the book.

Beirich said while most of the violence by people associated with National Alliance has been in the United States, the organization has always had a "global footprint."

"They do not define themselves by country. They define themselves by race," she said.

A Thomas Mair of Batley — the town where the suspect lives — was also named as a former subscriber to pro-Apartheid publication SA Patriot. In 2006, the online newsletter of far-right group the Springbok Club said Mair was "one of the earliest subscribers and supporters of SA Patriot."

Members of the Aryan National Alliance, formerly the Aryan Nations, salute supporters and protesters after parading through downtown Coeur d'Alene, Idaho, in this Oct. 28, 2000 photo. (Tom Davenport/Associated Press)

Cox was shot and stabbed outside a library in her northern England constituency. The suspect's brother, Scott Mair, told reporters his brother had a history of mental illness but was not violent.

Witnesses said Cox, a 41-year-old Labour Party legislator, was attacked by a man with a homemade or antique-looking gun. Clarke Rothwell, who runs a café near the scene, said the assailant shouted "Britain first" or "Put Britain first" several times.

Britain First is the name of a far-right group, which disclaimed any connection to the killing.

'Brexit' campaign postponed on both sides

Cox was a former aid worker who had championed the cause of Syrian refugees and campaigned for Britain to stay in the EU when it votes in a referendum on Thursday.

The referendum, sometimes known as Brexit, has sparked an intense debate about immigration and Britain's place in the world. "Leave" campaigners have said voters should quit the EU to take their country back from bureaucrats in Brussels and curb large-scale immigration from other EU nations.

Both sides in the referendum halted campaigning activity after Cox's death. Rival groups Britain Stronger In Europe and Vote Leave said they were cancelling rallies and major events planned for Saturday, though local door-to-door leafleting could resume.

In a show of political unity, Conservative Prime Minister David Cameron, centre, and Labour Party leader Jeremy Corbyn, right, visited the site of the killing 320 kilometres north of London. (Danny Lawson/PA via Associated Press)

Politicians from all parties have paid tribute to Cox, and Buckingham Palace said Queen Elizabeth wrote to her husband, Brendan Cox. The couple had two young children.

In a show of political unity, Prime Minister David Cameron and Labour Party Leader Jeremy Corbyn visited the site of the killing in Birstall, 320 kilometres north of London. The two men added bouquets to a huge mound of flowers left in tribute to Cox.

Cameron urged people to "value and see as precious the democracy that we have on these islands."

"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," he said.

Corbyn said the slaying of Cox was "an attack on democracy."

"It's the well of hatred that killed her," he said.

Corbyn said Parliament would be recalled from a break on Monday so that lawmakers could pay tribute to Cox. The House of Commons had not been due to resume meeting until after the referendum