David Gomoh, 24, was killed in Newham, east London – just before 10.30pm on Sunday.
His family were already in mourning after his father died from an illness linked to Covid-19 and were due to hold a funeral on Wednesday.
The 24-year-old was on the phone to a friend when he was attacked and police say there is no obvious motive for the stabbing. Marketing graduate Mr Gomoh worked for the NHS and his mother is a nurse.
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Detective Inspector Tony Kirk, of the Metropolitan Police, said: “David’s family are going through unimaginable torment. Within days his mother has seen the death of her husband and son, his sister has lost her brother and father, both are now heartbroken.
“David was a young man who had worked hard to put himself through university and, like his mother, worked hard for the community in the NHS.
“At this time we believe the only thing David did to be murdered was walk down a street. He was apparently approached by a group of men wearing masks and stabbed multiple times in a ferocious assault.
“I have no doubt this was a planned attack that singled out David because he happened to be in that area.
“David and his mother, who have done so much to help the community, now need the public to come forward and tell us what they know. If you have any information, please think of this young man and the suffering of his family and call us.
“If you don’t want to give your name, call Crimestoppers, but do make that call. David’s family deserve both answers and justice.”
Police believe the killers left the scene in a stolen Silver Dodge Caliber that was found abandoned minutes after the stabbing – half a mile away in Lincoln Road, Plaistow.
It had fake number plates and was seen being driven through a no entry sign from Cumberland Road.
Anyone with information can call police on 0208 345 3985 quoting CAD 8371/26APR, or, to remain anonymous, contact Crimestoppers on 0800 555 111 or online.