Jo Cox, the 41-year-old Labor Party member of Parliament for Batley and Spen who was killed Thursday, was elected to Parliament for the 1st time last year and swiftly made a name for herself on matters concerning immigration, refugees, and Britain’s membership in the EU.

Cox who is a supporter of Britain staying in the EU, was shot and repeatedly stabbed in her own constituency near Leeds in northern England by a man who witnesses said had shouted “Britain first”. A 77-year old man who is said to have attempted to help Cox was injured as well, however he is not in critical condition. The 52-year old suspect Thomas Mair is one of Cox’s own constituents and is said to have had a history of mental illness.

Mair has reportedly been a long-term supporter of Britain First, a far-right nationalist organisation which has for many years campaigned against immigration and Britain remaining in the European Union. Britain First leader Paul Goulding, former British National Party councillor, has denied that Mair has any connection with the organisation.

Mair has also been linked to Springbok Club, a white supremacist organisation which defends South Africa’s apartheid system. He has been named as one of the earliest subscribers and supporters of the organisation’s online magazine.

Cox had previously contacted police after receiving “malicious communications” and they had arrested a man in connection with the investigation in March, however he is not the man in custody for Thursday’s attack, a statement from London’s Metropolitan Police said.

Police said they were not in a position to discuss the motive of the attack.

Noting that her murder came one week before Britain holds a referendum on whether to stay in or leave the European Union, the killing of Cox prompted a halt to campaigning in the EU referendum until Monday next week, 20/6/2016. Although the motives of the killer were not instantly clear, some guessed that sympathy for Cox could boost the Remain campaign which has fallen behind Leave in recent days.

“Jo believed in a better world and she fought for it every day of her life with an energy and a zest for life that would exhaust most people,” Cox’s husband, Brendan, said.

“We have lost a great star. She was a great campaigning MP with huge compassion, with a big heart”, said British Prime Minister David Cameron.

U.S. Secretary of State John Kerry joined in expressing his deep sorrow for Cox loss; “It is an assault on everybody who cares about and has faith in democracy. And our thoughts are profoundly with the family – her husband, her children – and with all of the British people, who I know feel the loss profoundly”, he said.