And it adds weight to eyewitness claims he shouted "Britain first" or "put Britain first" as he allegedly attacked Ms Cox. Thomas Mair was convicted of Jo Cox's murder. Increasingly, the initial view of Ms Cox's death as the work of a mentally-disturbed loner is giving way to a picture of a right-wing political murder or act of terror. However new evidence also emerged of his troubled mental state, as the Telegraph reported Mr Mair sought help for his problems with depression the night before Ms Cox was killed - but was told to make an appointment and come back the next day. British police said on Friday that right wing extremism was a priority line of inquiry in their investigation.

West Yorkshire Police Temporary Chief Constable Dee Collins also said the attack on Ms Cox was believed to have been a targeted attack. A receipt that allegedly shows Thomas Mair, the man arrested over the killing of British MP Jo Cox, bought far-right wing and Nazi materials. He was said to be "lucid" under police questioning. However the political overtones of the attack led police to contact MPs around the country to give them security advice – and campaigning on the Brexit referendum remains suspended by both sides until Sunday. Tributes for Jo Cox in Parliament Square, London. Credit:Matt Dunham/AP

Commentators in the media and in politics have linked the attack to the raised emotions and anti-migrant sentiment aroused by the referendum. German chancellor Angela Merkel called on campaigners to moderate their language, saying that without respect for the beliefs of others "the radicalisation will become unstoppable". A car is removed for forensic testing near to where Jo Cox, Labour MP for Batley and Spen, was shot and stabbed outside Birstall Library. Credit:Christopher Furlong/Getty Images Labour MP Neil Coyle, a friend of Ms Cox, said Leave campaigners had put out "very dangerous" material that "risks inspiring extremist elements on the hard right in this country". But Rachel Reeves, also a Labour MP and friend of Ms Cox, said on Friday, "'We don't know what the motives were of the guy who attacked her yesterday. I don't think we should link the referendum to Jo's death."

Labour leader Jeremy Corbyn, front, is flanked by the MP for Leeds Central Hilary Benn, Prime Minister David Cameron and the Chaplain to the Speaker of the House of Commons Reverend Rose Josephine Hudson-Wilkin as they lay flowers in memory of Jo Cox. Credit:Christopher Furlong/Getty Images Labour MP Ben Bradshaw, who has suffered homophobic and racist abuse which culminated in a man being arrested on Thursday, said "I think we have to be careful not to prejudge the motive for this attack." However, people should think "about the political culture that we have in this country and how we nurture a kinder culture". Flowers have been left on the houseboat where Jo Cox lived in Hermitage Moorings on the River Thames in Wapping, London. Credit:Matt Dunham/AP "I think (MPs are) all aware of our vulnerability," he said.

The anti-extremist Southern Poverty Law Centre published receipts from 1999 and 2003 showing a Thomas Mair, of Batley, West Yorkshire, had bought books with titles such as Chemistry of Powder and Explosives, Improvised Munitions Handbook and Incendiaries. A flag flies half mast over Portcullis House, Westminster, in memory of Jo Cox. Credit:Dan Kitwood/Getty Images One book had instructions on how to build a homemade gun. He had also bought a copy of Ich Kampfe, a handbook from 1940s Germany that was given to new members of the Nazi Party, and Flashpoint, most likely a 1996 book speculating about the start of a third world war. He had subscribed to National Vanguard, the NA's magazine, a virulently anti-Semitic, racist publication which advocated creating an all-white 'homeland'.

The Guardian reported that police units who searched Mr Mair's house found "samples of Nazi regalia and far right-wing literature". On Friday the Telegraph reported that Mr Mair had visited an alternative therapy centre in Birstall on Wednesday evening, the night before Mrs Cox was killed, where he explained he wanted treatment for depression. The centre's owner Rebecca Walker, 42, told the Telegraph: "He came to the centre looking for alternative therapies for his depression. "He said he had been suffering from mental health problems for a long time, but said that reflex therapies and others he'd tried in the past hadn't helped. "He appeared to be quite a troubled man, didn't say very much to anyone while he was there.

"I asked him to come back on Thursday to discuss it all and have a drink, but he never came back. "You think maybe you could stop it, you know if he'd stayed for five more minutes. I guess I couldn't really have done much though really." Also on Friday, Ms Cox's assistant revealed her last words: "my pain is too much". Both PM David Cameron and Labour leader Jeremy Corbyn visited Birstall on Friday to lay flowers close to the scene of the killing and pay their respects. The prime minister said the whole nation was rightly shocked at Ms Cox's death, and called for people to "value, and see as precious, the democracy we have on these islands".