Hundreds Gather at London Vigil for Slain British Politician Jo Cox

Jo Cox was shot and stabbed in Birstall, England, on Thursday.

— -- Hundreds gathered in Parliament Square in London for a vigil for slain British politician Jo Cox, where speakers urged mourners to "unite against the hate that killed her."

Cox, a British Member of Parliament (MP) and mother of two, was killed in a shooting and stabbing midday Thursday after a town hall meeting in West Yorkshire, England.

Police search teams arrived this morning at the scene in the town of Birstall, where the investigation continues.

Officials confirmed to ABC News today that they were still questioning a 52-year-old suspect and were not looking for anyone else. The police have not released the suspect's name and the man's motives remain unknown.

Cox, 41, was an MP for the Labour Party. She was campaigning for the U.K. to remain in the E.U. and was known for her work on Syria-related issues.

The attack has raised concerns about security measures for British lawmakers. A spokeswoman for the prime minister's office said today that a reminder about safety guidance had been sent out.

Cox reportedly had been subjected to hate mail and police were poised to put extra security in place for her.

Vigils were held Thursday night as people lit candles and stopped to remember Cox outside Parliament and in her hometown in West Yorkshire.

Flags were flown at half-staff at Houses of Parliament this morning as the Buckingham Palace and other notable landmarks honored the slain politician.

Tributes have also poured in from across the political spectrum.

Conservative MP Andrew Mitchell wrote an emotional personal tribute in the Telegraph newspaper, describing her as "a five-foot bundle of Yorkshire grit."

"It's hard to believe that someone so brave and fearless and fun is dead, but the hardest thing to think about is her two lovely little children. They would come in to Portcullis House for tea with their mum, and now she’s gone," Mitchell wrote.

Campaigning in the referendum on Britain's membership in the European Union, which takes place on June 23, remains suspended.

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