Police shot dead Jihad Al-Shamie, 35, on Thursday outside the Heaton Park Congregation Synagogue in Manchester after he rammed a car into pedestrians, attacked some with a knife and tried to force his way into the building.
Congregation members Melvin Cravitz, 66, and Adrian Daulby, 53, died in the attack on Yom Kippur, the holiest day of the Jewish year.
Police say an armed officer accidentally shot Daulby as he and others barricaded the synagogue to block Al-Shamie from entering.
Three other men are in hospital with serious injuries.
Detectives say Al-Shamie, a British citizen of Syrian origin who lived in Manchester, may have been influenced by "extreme Islamist ideology".
He wore what appeared to be an explosives belt, which was found to be fake.
Police said Al-Shamie was on bail over an alleged rape at the time of the attack, but had not been charged.
Three men and three women, aged between 18 and their 60s, were arrested in the Greater Manchester area on suspicion of the "commission, preparation and instigation of acts of terrorism," as police work to determine whether the attacker acted alone.
The attack has devastated Britain's Jewish community and intensified debate about the line between criticism of Israel and antisemitism.
Recorded antisemitic incidents in the UK have risen sharply since Hamas' October 7, 2023, attack on Israel and Israel's ensuing war against Hamas in Gaza, according to Community Security Trust, a charity that provides advice and protection for British Jews.
Some politicians and religious leaders claim pro-Palestinian demonstrations, which have been held regularly since the war in Gaza began, have played a role in spreading hatred of Jews.
The protests have been overwhelmingly peaceful, but some say chants such as "From the river to the sea, Palestine will be free" incite anti-Jewish hatred.
Some also say the UK's recognition of a Palestinian state last month has emboldened antisemitism — a claim the government rejects.
Deputy Prime Minister David Lammy was interrupted by boos and shouts of "shame on you" on Friday as he addressed a vigil for victims of the attack in Manchester.
Israeli Prime Minister Benjamin Netanyahu and his supporters have frequently accused critics of Israel or its conduct of the war of antisemitism.
Critics see it as an attempt to stifle even legitimate criticism.
Pro-Palestinian demonstrators were held in Manchester and London on Saturday despite objections from police and politicians.
Prime Minister Keir Starmer said organisers should "recognise and respect the grief of British Jews this week" and postpone the protests.
About 100 people gathered in a central Manchester square in heavy rain, waving Palestinian flags and demanding an end to the war in Gaza.
In London, organisers said about 1000 people demonstrated against the banning of Palestine Action.
The direct-action group vandalised British military planes and targeted sites with links to the Israeli military.
It has been labelled a terrorist organisation by the government.
Police carried away several people who sat silently in Trafalgar Square holding signs saying "I oppose genocide, I support Palestine Action".
More than 1500 people have been arrested at similar protests since Palestine Action was proscribed in July, and more than 130 charged with terrorism offences.
Campaigner Jonathon Porritt said protesters would demonstrate huge respect and real grief for those affected by the absolute atrocity at Heaton Park.
"But I don't think that means that we should be asked to give up on our right to stand up for those who are being devastated by an ongoing, real-time genocide in Gaza," he told the BBC.
