The man accused of murdering Labour MP Jo Cox shouted "This is for Britain!" as he repeatedly shot and stabbed the mother of two as she made her way to a constituency surgery near Leeds, the Old Bailey heard.
Thomas Mair, 52, who denies the charge, showed no emotion as the postmortem findings were read out in court on Monday.
The jury heard Mair shot Cox three times with an adapted .22 German-manufactured Weihrauch bolt-action rifle, and used a "dagger like a knife" to inflict 15 stab wounds, some of which penetrated the MP's heart, lungs, stomach, and liver.
The court also heard that Cox, 41, had "through and through" gunshot injuries to her hands, which suggested she had used her hands to cover her face during the attack on 16 June in the run-up to the EU referendum.
Cox, who lived with her husband and children in a houseboat on the Thames, was attacked in Birstall, West Yorkshire – part of the Batley and Spen constituency she was elected to represent last year.
Richard Whittam QC, prosecuting, told the court how several witnesses heard Mair shouting words to the effect of "This is for Britain", and "Keep Britain independent" during his attack.
"It was a cowardly attack by a man armed with a firearm and a knife," Whittam said. "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'."
The MP was killed in "what was a planned and premeditated murder for a political and/or ideological cause," he added.
The prosecution said one witness, Fazila Aswat, heard the defendant shout: "Britain First. This is for Britain. Britain will always come first."
The court heard that witnesses watched Cox try to crawl away as Mair reloaded his gun and shot her a further two times.
Bystanders tried to intervene, including 77-year-old local man Bernard Kenny, who the prosecutor said was stabbed once in the abdomen by Mair.
The court heard that Mair was a regular visitor at his local library, where he would use the computer and internet facilities.
The jury were told how a police investigation revealed that Mair had browsed various right-wing online publications such as the Occidental Observer, which posts stories from a white nationalist and anti-Semitic perspective. He had also researched Nazi Germany and the Ku Klux Klan.
In the days leading up to Cox's murder, the jury were told, Mair had searched for Cox online, and looked at her Twitter page, then her Wikipedia page.
The court also heard how he accessed the Wikipedia page for Ian Gow, who was killed by the IRA in 1980 and who, before Jo Cox, was the last MP to be murdered.
After Mair's arrest, police searched his home and found material similar to the white supremacist and assassination material he was viewing online at the library. They also found part of a computer printout from Jo Cox's website.
Cox was the head of policy for Oxfam, a senior adviser to anti-slavery charity Freedom Fund, and chair of the Labour Women’s Network before joining parliament, where she was a committed campaigner for the people of Syria.
Mair is also charged with possession of an offensive weapon with intent, possession of a firearm with intent, and grievous bodily harm against 77-year-old Kenny. He denies all charges.
The trial, which is expected to last up to three weeks, continues.