The family of Duggan, shot dead by police on Thursday, said they were angered by the lack of information they received, and that their upset stoked tensions immediately before Saturday's riot in Tottenham.
The circumstances surrounding the death are being investigated by the Independent Police Complaints Commission.
The Metropolitan police apologised to the family on Monday, having earlier said that once the IPCC takes over an investigation, they also take over the role of family support.
Deputy assistant commissioner Stephen Kavanagh said: "I want to apologise to the Duggan family because I think both the Independent Police Complaints Commission (IPCC) and the Metropolitan Police could have managed that family's needs more effectively."
Rachel Cerfontyne, the IPCC commissioner leading the investigation, said: "I am very clear that their [family] concerns were not about lack of contact or support from the IPCC.
"Their concerns were about lack of contact from the police in delivering news of his death to Mark's parents. It is never the responsibility of the IPCC to deliver a message regarding someone's death."
She added that "if necessary" the complaint would become part of the IPCC's investigation.
Saturday's riots followed the family's long wait outside Tottenham police station to see a senior officer.
Cerfontyne pinned this error on the Met, saying the force waited too long before telling the IPCC the family wanted to see them. "I am also aware that Mr Duggan's family were unhappy at waiting at the police station for such a long time," her statement continued.
"The IPCC was contacted by the MPS [Metropolitan police service] at 8.30pm on Saturday evening. We were told that Mr Duggan's partner had been there and wanted answers to a variety of questions, but that she had now left."
Earlier the Met denied being in crisis over the two nights of rioting which saw them lose control of the streets and vowed to stamp out the disorder.
The acting Met commissioner, Tim Godwin, came close to admitting the force's handling of the aftermath of Duggan's death and the way it interacted with the community could have been better. "Events that led up to it, we need to look at," he said.
In his first public comments since the rioting broke out, Godwin said: "We will not stand by whilst criminality occurs on our streets in the evening."
He praised his officers who tried to quell the disturbances that have now blighted north, south and east London: "I was immensely proud, as I have always been, to be a member of the Metropolitan police service.
"The sheer bravery, the determination and the resilience of the men and women of the Metropolitan police could be seen from all the images that we had."
Kavanagh said those who smashed shops and looted on Sunday were younger, with some in their teens. They had used social networking sites to organise trouble.
"What you've seen is two distinctively different nights, the first one was based around the frustration of communities," he said, "while the second night was pure criminality."
People using social media such as Twitter to instigate violence would face investigation and prosecution and he condemned "inflamatory, inaccurate" messages, saying they would be pursued the same way as verbal threats and placards.
With more than 200 people now arrested, Kavanagh said a murder squad detective would lead the investigation into catching more rioters, which would rely on CCTV and information from communities furious at the rioters who were behind "disgusting behaviour, ripping apart people's livelihoods and businesses".
Police said knifes and machetes were looted from shops and used in attempted attacks on officers in Tottenham on Saturday night. It was a chilling echo of the 1985 Tottenham riots which saw PC Keith Blakelock become detached from colleagues and then killed by a mob.
Officers on Saturday had used their riot shields to protect themselves from the weapons. "People were trying to get around the shields to harm the officers," Kavanagh said.
Police said they had tripled the number of officers on the streets on Sunday compared to Saturday, after an outbreak of violence which they had not anticipated and they claim they had no forewarning of, despite people with close knowledge of the Tottenham area saying they warned police the shooting could lead to trouble on the streets.
On Monday night there were four times the amount of officers available as on Saturday, with forces bordering the capital asked for help.
Kavanagh defended decisions on Saturday that left looters in control of Wood Green for several hours. He said police commanders had to decide where best to deploy their resources, prioritising Tottenham High Street, the scene of the worst clashes.
Kavanagh denied London's streets had been "left" to the looters and said his colleagues were making rapid decisions in a "difficult, rapidly escalating situation".
Within the last few weeks the Met has lost commissioner Sir Paul Stephenson and assistant commissioner John Yates over the phone-hacking scandal.
Concern about "resilience" in the Met – that is, its ability to cope with a series of big events – led the home secretary to second Bernard Hogan-Howe as temporary deputy commissioner from Her Majesty's Inspectorate of Constabulary.
Professor of Economics
2004-2006 Alfred P. Sloan Research Fellow
Office: 3115C Tydings Hall
Tel: (301) 405-3532
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Department of Economics
University of Maryland
College Park, MD 20742
Mark Duggan, Professor, received his B.S. and M.S. in Electrical Engineering from M.I.T. in 1992 and 1994, respectively, and his Ph.D. in Economics from Harvard University in 1999. His primary fields of interest are public finance and health economics. His current research focuses on theoretically modeling and empirically estimating the effect of government expenditure programs such as Social Security, Medicare, and Medicaid on the behavior of individuals and firms. He was a Fellow of the Alfred P. Sloan Foundation from 2004 to 2006 and his research is currently being supported by the NIH and the NSF. He teaches public finance at both the graduate and the undergraduate level.