Tributes have been paid by the “heartbroken” families of three men who were stabbed to death in a park in Reading on Saturday.
James Furlong, David Wails and Joe Ritchie-Bennett died in the attack.
The PM sent his “deepest condolences” to their families, describing the attack as “abject cowardice”.
Police continue to question suspect Khairi Saadallah, 25, who came to the UK from Libya in 2012. He was arrested under the Terrorism Act.
Mr Wails, a 49-year-old scientist who specialised in clean energy, was the last victim to be named.
His parents said he was a “kind and much loved son, brother and uncle who never hurt anyone in his life”.
“We are broken-hearted at losing him and in such a terrible way,” they said.
His employer, metals and chemicals firm Johnson Matthey, described him as “a gentle, thoughtful man with a dry sense of humour” who was “proud to use his expertise to make a positive impact on the world”.
Friend Michael Main said he “always made people smile”.
Mr Ritchie-Bennett, 39, was originally from Philadelphia but had lived in the UK for 15 years.
His father, Robert Ritchie, said the family were “heartbroken”, while his brother-in-law, Stephen Bennett, and sister-in-law, Katy Bennett, said he was “the most kind, caring and loving person that you could meet”.
BBC Radio Berkshire presenter Sarah Walker said Mr Ritchie-Bennett had been married to her close friend, Ian, who died from cancer nearly six years ago.
She described him as a “fantastic human being” who was “outrageously funny”.
Mr Furlong, 36, was a teacher and head of history, government and politics at The Holt School in Wokingham.
His parents Gary and Janet described him as “beautiful, intelligent, honest and fun”.
“He was the best son, brother, uncle and partner you could wish for,” they said.
Speaking in the Commons shortly after a minute’s silence was held in Parliament, Prime Minister Boris Johnson paid tribute to the three victims.
“To assault defenceless people in a park is not simply an act of wickedness but abject cowardice, and we will never yield to those who seek to destroy our way of life,” he said.
More than 100 students, some holding hands, gathered at the gates of The Holt School for a two-minute silence on Monday morning, while a flag in the courtyard was lowered to half-mast.
Former pupils and parents have asked for the school’s humanities block to be renamed in Mr Furlong’s memory.
Mourners also gathered for a one-minute silence outside the Blagrave Arms pub in Reading town centre, where the three men were regular customers.
It was described as a “safe space” for members of the LGBT+ community.
A tribute on the door called them “the kindest, most genuine, and most loveliest people”.
Martin Cooper, chief executive of LGBT+ charity Reading Pride, described the three men as “true gentlemen”.
“They were a support network for individuals, and I know they will be sorely missed by many,” he said.
Police were called to Reading’s Forbury Gardens at about 19:00 BST on Saturday.
Witnesses say a lone attacker with a knife shouted “unintelligible words” and stabbed several people who were in a group.
Three other people who were injured in the attack have since been discharged from hospital, police said.
The suspect, Mr Saadallah, was initially arrested on suspicion of murder. He was later re-arrested on Sunday under Section 41 of the Terrorism Act 2000.
Under the Act, police have the power to detain him without charge for up to 14 days.
Mr Saadallah originally claimed asylum and was given leave to remain in 2018, the BBC’s Home Affairs correspondent Daniel Sandford said.
He came to the attention of MI5 last year as someone who might travel overseas, possibly for terrorism purposes, but they assessed that he was not a genuine threat or an immediate risk.
A close member of his family told the BBC that he left Libya to escape the violence there, and that he had suffered from post-traumatic stress from the civil war. However, he had been thinking of trying to return.
They said his long-standing mental health problems had been exacerbated by the coronavirus lockdown.
Neighbours said Mr Saadallah threw a TV from his top-floor flat this year and had a mental health key worker.
In a statement, his brother, Aiman Saadallah, said: “We are all shocked and deeply saddened by this senseless attack.
“I want to express our condolences to the families of the victims that have died and wish a speedy recovery for all those injured.”
Counter terror police, who are not looking for anyone else in connection with the incident, have said they are “keeping an open mind as to the motive for this attack”.
They are continuing to appeal for information.
After visiting Reading to lay flowers on Monday morning, Home Secretary Priti Patel told MPs the threat posed by lone attackers was “growing”.
She thanked those who responded to the incident, including student police officers – noting that a “young, unarmed” officer “took down the suspect without hesitation” while another carried out first aid.
Shadow home secretary Nick Thomas-Symonds said it was “heartbreaking that we are having this conversation again so soon” after attacks at Fishmongers’ Hall near London Bridge in November and in Streatham in February – adding that the public “will want answers”.
He previously said that with the Ministry of Justice’s budget having been cut by 40% over 10 years, the government needed to reconsider the resources available for de-radicalisation programmes in prisons, as well as monitoring, supervision and risk assessment of released prisoners.