Two detectives have been told to resign for not properly investigating a knife attack on a father who was then killed.
Peter Woodhams was first attacked in January 2006
A misconduct hearing found the pair had not followed up evidence prior to the murder of Peter Woodhams, 22, from Canning Town, east London.
He was shot dead outside his home in August last year after a seven-month campaign of violence and bullying.
An Independent Police Complaints Commission (IPCC) inquiry found "serious flaws in the police response".
A detective sergeant and a detective constable have been ordered to resign over the issue.
IPCC findings on police inquiry
Officers failed to bring in forensic experts
No photographs were taken of the scene
A proper record of the attack was not made in officers' pocketbooks
Officers failed to contact the Woodhams family for more information
Anonymous phone calls identifying several suspects were not followed up by police
Two sergeants did not adequately manage the scene of the attack
Mr Woodhams first encountered trouble after he confronted hooded youths who were throwing stones.
The youths stabbed him in the neck and slashed him across the face in January 2006.
Ten days after the attack, Mr Woodhams told officers: "This has had a dramatic effect on my life. I can't go out anymore because I am scared."
But despite this, officers failed to secure evidence, take statements or pursue leads, the IPCC inquiry found.
Months later, the young father was shot on the doorstep of his east London home.
In May, 18-year-old Bradley Tucker was jailed for life at the Old Bailey for the murder.
Tucker was jailed for Mr Woodhams' murder
Mr Woodhams' father, also called Peter, criticised police officers over the earlier attack.
He said: "I get no pleasure out of this at all, it's not going to bring my son back.
"But if we can stop this happening to one other family it will bring some comfort."
Changes to procedures for supervising investigations in the borough of Newham have been made since the stabbing investigation, the IPCC said.
Commander Mark Simmons, from the Metropolitan Police, said: "It continues to be a matter of deep regret for us the family of Peter Woodhams suffered further anguish because of shortfalls in this investigation.
"We did not meet the standards expected of us or that we expect of ourselves. We have since taken steps to implement changes to improve and modify how Newham as a borough and the Metropolitan Police as an organisation, deal with allegations of violent crime."