The last words of Jo Cox were "No, my pain is too much", the father of the MP's assistant has said.
Ghulam Maniyar said his daughter, Fazila Aswat, had tried to help the politician as she lay dying in her arms.
Ms Cox, a 41-year-old mother-of-two, was shot three times and repeatedly stabbed by a man screaming "Britain first".
Police arrested a 52-year-old former psychiatric patient named locally as Tommy Mair.
As she lay bleeding to death, he repeatedly kicked her before walking away, having stabbed a 77-year-old man who tried to intervene.
Ms Aswat had urged Ms Cox to get up, but the pain was too much, according to the former Labour councillor.
"She said her injury was so bad and she was in her arms. There was lots of blood," he told ITV News.
"She said, 'Jo, get up', but she said, 'No, my pain is too much, Fazila'. And I think those were the last words Jo spoke."
Mr Maniyar said his daughter had tried to stop the attack and is "in shock".
"She tried to help her, she tried to hit the attacker with her handbag, but he tried to go at her," he said.
"People came, so he followed them and he came back again and shot her again twice.
"My daughter, she's in shock because she's been with Jo for one year and working very closely with her. It will take time to fully recover from the shock.
"She knew that Jo was very badly injured. That's why she's not speaking about everything she's seen. She lost one of her best people."
Mair, who was arrested in connection with the murder, is reported to have bought a book off the internet about making a homemade gun, it has been claimed.
According to records obtained by the Southern Poverty Law Centre, he is alleged to have bought a "munitions handbook" that included detailed instructions on how to build a pipe pistol in 1999.
The manual was being sold at the time by the National Alliance, a white supremacist organisation founded by William Pierce in 1970 and aimed at creating an all-white homeland.
Based in West Virginia, the organisation reached its peak in the 1990s but fell away in the years after Pierce's death in 2002, though it has been "reconstituted".
Mair was arrested on suspicion of murdering Ms Cox, who died outside a library in Birstall, West Yorkshire, where she was due to hold a constituency surgery.
Witnesses had reported seeing the attacker reload the gun between each shot. One said the gun was either antique or home-made.
The first murder of a British MP for more than a quarter-of-a-century prompted widespread revulsion and led to the suspension of campaigning for Britain's EU referendum.
Police will investigate whether Ms Cox, a Cambridge graduate and former adviser to Gordon Brown's wife Sarah, was targeted because of her support for the Remain campaign.
The MP for Batley and Spen since only last year, she had spoken out against the "racism and fascism" of Britain First, an anti-Islam right-wing group.
Meanwhile, there was a minute's silence and vigil at Dublin's Custom House last night as dozens gathered to express solidarity with the family and friends of slain Ms Cox.
"Today we send a message that love must overcome hate," said organiser and human rights activist Dan O'Neill,.
Former TD for Dublin Central Joe Costello said he believed that the MP's tragic death had shades of the murder of Irish journalist Veronica Guerin.
"A line has been crossed… this isn't something that should have ever happened," he added.