The police watchdog said it is following “a number of significant lines of inquiry” surrounding the death of Mark Duggan in north London.
Rachel Cerfontyne, deputy chairwoman of the Independent Police Complaints Commission, said the body is trying to speak to key witnesses who have either so far refused to be interviewed or who have given conflicting accounts.
The watchdog is also looking at the way police dealt with intelligence connected to the 29-year-old before he was gunned down, in the wake of criticism by the jury at the inquest into Mr Duggan’s death.
Ms Cerfontyne said: “Having assessed the evidence at inquest, there are initially a number of significant lines of inquiry which we are pursuing.
“These include following up concerns about the way the police responded to intelligence and seeking to interview some key witnesses who have so far declined to speak to or be interviewed by us or whose accounts are inconsistent with other evidence.
“We expect police officers to cooperate fully with us if required, including answering questions at interview, something they have so far refused to do.”
Mr Duggan’s family and their lawyers met with chairwoman of the IPCC Anne Owers and Ms Cerfontyne on Tuesday to discuss the watchdog’s investigation.
Relatives of the father-of-six were left furious at the inquest finding that he was lawfully shot by police, despite not having a gun in his hand at the time.
The IPCC was also heavily criticised for failing to contact his family in the immediate aftermath of the shooting, and for initially wrongly telling journalists that he had fired a shot. Ms Cerfontyne added: “We know that the family’s confidence in us and our investigation was damaged by mistakes made in the early stages – both in relation to inaccurate information we provided to the media, and the initial management of the incident.”
Mr Duggan was shot by a police marksman after armed officers stopped the taxi in which he was travelling in Tottenham in August 2011.