An 18-year-old has been arrested over the death of law student Hussain Chaudhry, 18, who was fatally stabbed in east London on Wednesday.
The Metropolitan Police said the man was arrested on suspicion of murder and taken to an east London police station on Friday evening.
He remains in custody as police continue to investigate the stabbing of Mr Chaudhry outside his family home in Leyton, east London, on Wednesday evening.
Police were called at around 5.20pm to reports of a stabbing and Mr Chaudhry was pronounced dead at the scene at 6pm.
Friends said Mr Chaudhry was selling designer jackets worth a few hundred pounds and the attack was likely part of a deal gone wrong.
His mother and brother suffered slash injuries to their hands, with a woman in her 40s still in hospital, while a man in his 20s has since been discharged, the Met said.
Hussain Ahmed Chaudhry (pictured), 18, was killed outside his home in Leyton, London , on Wednesday night in an altercation that saw his mother and brother's hands slashed with a knife
The force previously said that a post-mortem examination on Thursday gave Mr Chaudry's cause of death as hypovolemic shock and a stab wound to the neck.
Mr Chaudhry's family said in a statement: 'We are deeply grieved by the loss of our beloved Hussain and respectfully ask for the privacy and space to come to terms with this tragic situation.
'We thank everyone from the bottom of our hearts for their kindness, compassion, condolences, prayers and goodwill. We have no other comment at this time.'
Detective Chief Inspector Perry Benton, from the Met's Specialist Crime Command, said: 'A young man has lost his life in tragic circumstances and my thoughts remain with his family and friends at this awful time.
'I am continuing to appeal for any witnesses to come forward and speak with my team. Any piece of information could prove to be vital.'
Hussain was killed outside his home in Leyton, London, in an altercation that saw his mother and brother's hands slashed with a knife. Pictured, flowers left outside the house
He said additional officers will be in the area over the coming days to help reassure the community and listen to concerns from residents.
A 16-year-old boy who was arrested on Wednesday has been released under investigation.
Mr Chaudhry's sister Afia earlier said on an online fundraising page that her 'beautiful baby brother left this world the same way he came in, cradled in my mother's arms'.
She called him 'the sunshine of my life' as she paid tribute to him on social media, writing: 'We've lost our baby and no pain will compare. The sunshine of my life. My youngest brother, Hussain.
Police officers at the scene as a murder investigation was opened
'You radiated light & never had anything but a smile adorning your face. You studied well, loved well, prayed well.
'Fly with green birds, my martyr. Meet me by at the gates of Jannah, will you? I'll wait to your familiar face.'
Mr Chaudhry's friend Wahab Ahmed, who set up the page to build a mosque in his memory, described him as an 'incredibly kind and beautiful soul'.
More than £27,000 in donations has been raised by the GoFundMe page set up in Mr Chaudry's memory at gofund.me/e98c8e95.
Soas University of London said in a earlier statement it was 'shocked and deeply saddened' to learn of Mr Chaudhry's death.
A close friend who went to college with Mr Chaudhry said he loved football and was a big Manchester United fan.
He said: 'We went to college together and he was in my 3D design and maths class.
'He was one of the first people I became friends with on the first day. I remember he was sitting across from me and smiled because I'd purposefully sat next to this girl.
The family were selling designer clothing worth a few hundred pounds and a neighbour, who did not want to be named, described how one of the men involved in the altercation was punched in the face before he grabbed the jacket and fled. Pictured, a tent at the scene
'He was a big Manchester United supporter and because I support Arsenal, we would bet five pounds each time they played.
'It was his birthday in two weeks (April 2) - he had his whole life ahead of him and had just started uni.
'He was quite quiet and reserved, but really approachable. I haven't fully comprehended that he's gone, like I'm still expecting him to call me and say let's go for a haircut.'
Detective Superintendent Paul Whiteman said extra officers will be in the area over the coming days to help reassure the community and listen to concerns from residents.
He said: 'We remain committed to tackling violent crime and we are working with a number of partners to help us prevent another tragic loss of life.
'You will see extra officers in the area this week and they will be using a range of tactics to target those who choose to put others in danger by carrying a knife.'
DCI Benton said the victim's mother and brother suffered serious hand wounds.
Speaking at the scene, he said: 'On Wednesday, March 17, at around 5:20 pm an altercation took place inside the house, which then spilled out onto the street.
'During the incident unfortunately Hussain was fatally stabbed and during the same incident his mother and brother received serious hand injuries.
'They are serious hand injuries - I mean the mother's still in hospital so it shows the seriousness of it.
'It's truly shocking and it's really impacted the community and obviously the family are devastated.
'There's a lot of information going round on social media and I would like to appeal to people not to speculate about those responsible at this time.
'At the moment we're working on the assumption that there were two males involved.
Police at the scene of Hussain's death Wednesday night as investigations continued
'It's a tragedy for the family and my heart goes out to them.
'I'm sorry for their loss. We're doing everything we can to identify those responsible and try to bring them to justice.'
A neighbour, who did not want to be named, described how one of the men involved in the alleged altercation was punched in the face before he grabbed a jacket and fled.
The thug was thought to have ordered a taxi before deciding to run across rooftops at around 5.20pm.
Reiss Chaudhry said his nephew died in his mother's arms.
School friends who laid flowers for the teenager said he was a kind-hearted and bubbly person who was good at everything.
He was studying law in his first year at SOAS University in London after attending Leyton School secondary school.
Speaking at the scene, his uncle Mr Choudhry said: 'He was just trying to protect his mum. He was a good boy and such a lovely boy.
'His mum was badly cut across her hand and his brother was hurt too and they are both still in surgery. He was stabbed in the neck and he died laying in his mother's lap.'
School friends who laid flowers for the teenager said he was a kind-hearted and bubbly person who was good at everything. Pictured, the family home
Tests are carried out at the scene by forensic officers after an 18-year-old died
Flowers have been lined up outside the teenager's terraced home since Thursday.
One 19-year-old woman said: 'He was very bubbly, very kind-hearted and a big family man. He cared a lot about his family. He had a great aura about him.'
Another woman, also 19, said: 'He was lovely, funny, caring, and good at everything. He had a great personality. He was studying law at university in his first year.'
According to neighbours, Hussain's father owns a property business.
A 35-year-old man, who did not wish to be named, tried to save Hussain after he fell to the ground.
Two nurses returning from their hospital shift started CPR in the street before the teenager was pronounced dead just after 6pm.
A neighbour said: 'This is all over a designer jacket, who kills over a jacket? The family were selling designer jackets online and two kids turned up to rob it.
Police equipment litters the tarmac in the middle of a road in Leyton, east London
'The lad who died was stood on the cycle path. He made in the direction of where the attacker ran off but then he stumbled and fell to the ground where he'd been stabbed already.
'I tried to take the pulse of the kid but I couldn't find anything.
'His eyes were wide, he was staring off a thousand yards and all the blood had drained from his face.
'Then two nurses returning from the hospital jumped on him and started doing chest compressions. This is getting out of hand in London, this is ridiculous.'
The neighbour added that the family did not have links with gangs.
In a statement about the killing, the local mosque named the victim as part of the Chaudhry family. Pictured, the scene Wednesday night
He added: 'They are a good family, that's their family home and they are not associated with any gangs.
'They donate a lot of money to the mosque and they are a respectable family within the Islamic community. One of the sons is involved with Walthamstow Forest Council.'
In a statement about the killing, the local mosque named the victim as part of the Chaudhry family.
A statement released by the Faizan e Islam mosque said: 'It is with great sadness and heavy heart we announce that son of Zahoor Ahmed, Hussain Ahmed Chaudhry, has departed from this temporary Dunya.
'May Allah elevate his status, grant him a lofty status in Jannat-ul-Firdaus and make his grave a garden from the Gardens of Paradise.'
Stella Creasey, Labour MP for Walthamstow, tweeted: '18-year-old male with a stab wound to his neck.
'CPR was performed but unfortunately not successful and life was pronounced at 6.08pm. Two family members have been taken to hospital with non-life threatening injuries.'