Exclusive poll: EU support falls after Jo Cox murder

British support for remaining in the European Union has weakened in the wake of the murder of the pro-EU politician Jo Cox, according to an online research company Friday.

Qriously, a London-based technology start-up that gathers data and intelligence about consumers through mobile phone apps, found that backing among likely voters for Britain's EU membership has dropped to 32% from 40% before her death.

The poll was based on 1,992 British adults surveyed on June 13-16, and then 1,002 on June 17 — the day after Cox was shot and killed in northern England. The start-up claims to have held the first such survey on the topic since the lawmaker's slaying. Most of Qriously’s surveys are done for corporate brands and it has not been previously conducted an EU referendum poll.

Respondents were asked: "Imagine the EU referendum were held today. Would you vote for the U.K. to remain a member of the European Union, or leave the European Union?" They were given three options: "Remain in the EU," "Leave the EU," or "Don't know."

Qriously found that 52% will vote to leave the bloc in a national referendum on June 23. The figure is unchanged from before the parliamentarian's death. The weakening support for remaining in the EU coincided with a large move toward "Don't know," which leaped to 16% from 9% before Cox's assassination.

Britons are split over whether to leave the political bloc, but a series of recent polls — all conducted prior to Cox's death — have shown the Leave campaign gaining ground in the closing stages of the race. Political analysts have expressed uncertainly over how Cox's killing would affect the vote. She was an ardent EU supporter.

Tommy Mair, a suspect in the case who has been arrested but not charged, had ties to far-right, anti-immigration and anti-EU groups.

Stephan Shakespeare, the founder and chief executive British polling firm YouGov, told USA TODAY he did not think Cox's murder would lead to a shift in attitudes toward the vote, "but the nature of the campaigning will be changed and that probably will have an impact" on opinion.

"What tends to happen when you have an event of this kind is that the voices of those who feel they are affected by something become quieter. They don't change their minds."

Shakespeare said that the Leave campaign "will have wanted to go very hard on the immigration issue in the final week of the campaign and may find it hard" to do so now. "The Remain camp doesn't really need to be more polite because it doesn't want to talk about immigration. It wants to talk about the economy, where it is much stronger," he added.

The major British polling firms, including YouGov, were expected to release their first EU opinion surveys following Cox's murder over the weekend.