Killing of Anti-Brexit MP Puts Britain Campaigning on HoldThe shooting death of a British Member of Parliament a week before Britain votes on a hotly debated referendum on whether to quit the European Union stunned a country where gun attacks are rare and political violence is almost unheard of. Some witnesses say the alleged killer yelled "Britain first" as he shot, stabbed and kicked Jo Cox, a junior Labour Member of Parliament. The 41-year-old mother of two and former aid worker was known for her advocacy for Syrian refugees, her pro-immigrant stance and, most notably, her opposition to a British exit from the EU. She died after paramedics came to her rescue in her West Yorkshire district Thursday. Police are investigating, and government officials were cautious not to qualify the killing Thursday as being politically motivated. Police say they arrested one suspect and have not established a motive. They are not looking for any other suspects. Britain's Home Secretary, Theresa May, said she would not comment on the case until the facts are fully established. She called the decision to suspend campaigning on the referendum "entirely appropriate." 'Unusual event' Such violence involving a politician is very rare in Britain. "It's a very unusual event within the confines of British politics," Tony Travers, a political science professor at the London School of Economics, told VOA. Both opponents and supporters of Britain leaving the EU suspended their campaigns Thursday. Analysts say the decision was necessary, especially given the heated nature of the debate in the final days. The debate has been bitter, pitting British voters against one another on issues of immigration, sovereignty and trade. "This debate on EU membership shouldn't be embroiled in a situation like this. This has no place in any civilized society, and for it to be misplaced, maybe, into the debate would distort the fabric of the debate and do the debate injustice," said Rory Broomfield, director of The Freedom Association, a London pressure group that favors leaving. Reaction British Prime Minister David Cameron suspended campaigning in Gibraltar following the news of the attack on Cox. He called her death a "tragedy," and described her as a "committed and caring" member of parliament. Cameron said it was "absolutely tragic and dreadful news." Labour Party leader Jeremy Corbyn expressed shock at what he called "a horrific murder." Corbyn described Cox as having a "deep commitment to humanity," one who was "universally liked" at Westminster" and "who did her public duty right at the heart of our democracy." U.S. Secretary of State John Kerry said during a visit to Copenhagen that the attack on Cox is an attack on democracy. "It is an assault on everybody who cares about and has faith in democracy." Shock waves spread through Europe, where the events leading up to the Brexit referendum are being closely watched. European Commission President Jean-Claude Juncker tweeted that he was "deeply shocked" by news of what he called a "terrible attack." Cox had been vocal in her support for remaining in the European Union, posting many articles online, many of them in favor of continued immigration — one of the biggest and most contentious issues in the debate. In a recent appeal on Twitter, she invited readers to see a video on "why our great, proud nation should lead Europe — not Leave Europe."