Samuel Luiz, 24, was attacked while out with friends in the city of A Coruña in the early hours of Saturday morning after an argument started outside a nightclub. He died later in hospital.
Mr Luiz lost his life after a row with passers escalated into a fatal assault.
When he made a video call outside the club, two passers by accused him of trying to film them and he was assaulted by one of them.
He was left with a badly bruised face but minutes later the attacker returned with 12 others who beat the student nurse unconscious. He died hours later.
The attack, which is being investigated by police, prompted outrage across Spain and led to demonstrations on Monday night in Madrid, Barcelona, Valencia, Salamanca, Bilbao, Zaragoza.
Protesters carried signs reading: “No more deaths for hate, intolerance or discrimination.”
Diego Rubio, 21, who joined the demonstration in Madrid, carried a poster reading: “They have robbed us of our adolescence, now they rob us of our lives.”
The demonstration in Madrid erupted into clashes between riot police and protesters, prompting demands from politicians in the capital for explanations.
Spanish Prime Minister Pedro Sánchez condemned the killing and offered his condolences to Mr Luiz’s friends and family.
“I’m confident that the police investigation will soon find those who murdered Samuel and shed light on what happened,” he tweeted.
“It was a savage and merciless act. We will not take a step backwards when it comes to rights and freedoms and Spain will not tolerate this.”
Max Luiz, the father of the victim, said: “They have put out our only light. I just hope that his death is not in vain.”
Flowers and other tributes were left at the spot where Mr Luiz was attacked in A Coruña.
One message said: “They will have to pay for this crime Samuel.”
José Miñones, the Spanish government representative in Galicia, said police were investigating if the attack on Mr Luiz was motivated by homophobia.
Spanish police said on Tuesday they had arrested three men over the killing. Between five and twelve males were suspected of taking part in the fatal attack.
In a separate incident in Sant Cugat, a town north of Barcelona, a man was attacked after he refused to hand over his telephone and give cigarettes. He was called pejorative names associated with homophobia on a number of occasions, police said.
He suffered a broken tooth, bruises on his arm and legs and head.
The Mossos d’Esquadra, the Catalan regional police, said they were keeping an open mind as to the motivation but said it could be a hate crime.
The killing of Mr Luiz came less than a week after Spain’s annual Pride celebrations and days after Mr Sánchez’s left-wing government approved a draft law to protect and strengthen the rights of LGBTI+ people.
Spain’s Interior Ministry data showed 278 hate crimes related to sexual orientation or gender identity in Spain in 2019, an 8.6 per cent increase on the previous year.
The European Union Agency for Fundamental Rights warns only a fraction of hate crimes are reported to police.
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