Labour MP Jo Cox has been shot and stabbed to death for a “political and/or ideological cause“,
Thomas Mair, 53 years old, allegedly murdered Mrs Cox outside her constituency surgery in Birstall, near Leeds, on 16 June.
He shouted “Britain First” as he carried out the attack and researched a “far right” online publication in the weeks leading up to the killing, jurors were told.
Mr Mair, from Birstall, denies murder.
The court heard 41-year-old Mrs Cox was to hold a surgery in a library after visiting a local school and care home when she was attacked.
Prosecutor Richard Whittam QC said: “As she arrived she was brutally murdered by one of her constituents, this defendant”, Thomas Mair.
“It was a cowardly attack by a man armed with a firearm and a knife”.
“Jo Cox was shot three times and suffered multiple stab wounds. During the course of the murder Thomas Mair was heard by a number of witnesses to say repeatedly ‘Britain First“.
Mrs Cox was killed “in what was a planned and pre-meditated murder for a political and/or ideological cause“, Mr Whittam added.
Jurors were told that a 77-year-old man was also injured as he tried to save Mrs Cox.
Items found at Mr Mair’s home showed he had a “strong political and ideological interests,” Mr Whittam said.
The court heard he used computers to look up websites at the same library where Mrs Cox was due to hold her surgery.
In May he access the Wikipedia page of an online publication called the Occidental Observer – a “far-right” publication “that covers politics and society from a white nationalist and anti-Semitic perspective“, the prosecutor said.
Jurors heard in the days leading up to the killing he also looked at Twitter and Wikipedia pages for Mrs Cox and went on to view information on former Foreign Secretary William Hague.
And he viewed websites on Nazi material, the death penalty in Japan, political prisoners and the human liver and spinal column.
Finally, on the eve of the attack, prosecutors say Mr Mair researched right-wing politicians as well as the Ku Klux Klan and civil rights activists killed by its supporters.
Cox was a self-proclaimed “proud Yorkshire lass” whose work for charity took her around the world and whose political success led her to Westminster.
The 41-year-old mother-of-two was elected as MP for Batley and Spain in the 2015 election and increased Labour’s majority to 6,051 (from 4,406 in the 2010 election).
She described herself as “proud and humbled” to be the Labour MP for the place where she was born.
Mrs Cox first worked in politics after graduating from Cambridge University in 1995, but then built a career working for charities including Oxfam, Save the Children.
She was described by Labour leader Jeremy Corbyn as “a much loved colleague, a real talent and a dedicated campaigner for justice and peace.”
Jurors were shown CCTV footage of the defendant making his way along the road after leaving his home on the day of the killing.
The court heard Mrs Cox arrived for her surgery with her manager Fazila Aswat and senior caseworker Sandra Major.
Mr Mair attacked the Labour MP two minutes later in what the prosecution described as a “dynamic, fast-moving and shocking incident“, jurors were told.
They heard that passer-by Shelly Morris reported hearing “a loud bang like a popping sound” and a “loud piercing scream“.
She said she saw a man with a large steak knife with a jagged blade which he wielded in a “stabbing motion“.
Mr Mair denies Mrs Cox’s murder, grievous bodily harm, possession of a firearm with intent to commit an indictable offence and possession of an offensive weapon – a dagger.
The trial is expected to last for up to three weeks.