Floral tributes and candles are placed by a photo of slain Labour MP Jo Cox at a vigil in Parliament Square in London, on Thursday, June 16, 2016. Daniel Leal-Olivas/AFP/Getty Images

UPDATE: 12:21 p.m. EDT — Police told reporters Jo Cox, a member of the British Parliament, died Thursday from injuries suffered in an attack by a man who shot and stabbed the politician. She was 41.

The Labour Party politician had pushed for the United Kingdom to remain in the European Union ahead of the Brexit vote next week. Witness accounts reported Cox was attacked by a man yelling “Britain First.”

Original story:

The Thursday shooting and stabbing of a member of Parliament was likely related to next week’s scheduled referendum on whether the United Kingdom should remain in the European Union. A witness told the Telegraph Labour MP Jo Cox was assaulted in Birstall, England, by a man who shouted, “Britain First, Britain First, Britain First.” Another witness told the Independent a similar story.

A 52-year-old man was arrested in the attack, the BBC reported. Clarke Rothwell, a local cafe owner, told the news outlet the man was wearing a white baseball cap, a jacket and had “an old-fashioned-looking gun in his hand.” Rothwell told the BBC the man shot Cox multiple times and stabbed her with a hunting knife.

Helen Joanne "Jo" Cox MP | InsideGov

Cox, 41, has been very vocal in her campaign against a Brexit and has urged British citizens to vote in favor of remaining in the EU. She was meeting with constituents Thursday before the incident, which left her in critical condition. On the surface, the attack seems to indicate the assailant disagreed with Cox’s stance on a Brexit.

A good portion of Cox’s Twitter feed is filled with articles promoting arguments to stay in the EU. Less than a week ago, she tweeted out a video promoting the idea that Britain should remain.

The same day, she tweeted a photo of herself with local citizens and another politician campaigning ahead of the Brexit vote. They held “vote remain” and “in” signs, with Cox’s tweet using the hashtag “#StrongerIn.” She also tweeted a photo apparently showing her husband and children participating in a flotilla on the River Thames supporting the “in” movement.

Some who have pushed for Britain to leave the European Union have expressed concerns over the country’s increased immigration rates. Cox previously said on Twitter, “Immigration is a legitimate concern, but it’s not a good reason to leave the EU.”

The tweet accompanied an opinion piece she wrote about immigration and Brexit. It read, in part, “First, because leaving the EU won’t solve the problem. Over half of all migrants to Britain come from outside the EU, and the result of this referendum will do nothing to bring these numbers down.”

Her piece for the Yorkshire Post detailed why she had chosen “remain.” While she acknowledged immigration is a fine concern, she argued leaving wouldn’t fix the issue and that it would also be terrible for the economy.

She wrote:

"And finally – and perhaps most importantly – the overall benefits of EU membership are huge. While the “leave” camp are trying to distract voters, their economic case has been completely demolished by everyone from the president of the United States to small and medium businesses in Yorkshire. On this there is no doubt. Leaving the EU would hurt Yorkshire businesses and hit our own pockets."