Detectives have identified four men they believe may have been involved in the murder of former soldier Warren O'Connor -- though one is thought to have already fled the country.
Officers have made significant advances in their investigations and now believe they know who fatally plunged a knife into his chest.
Mr O'Connor, who has been described as a "hero", was murdered after he came to the aid of a pregnant friend, her partner and their young child.
He had attempted to intervene in a dispute among neighbours in Donaghmede over a loud party but was then chased by thugs who rammed his car before attacking him with a knife.
It is understood gardai have already interviewed one of four men they believe were at the scene during or shortly after the murder.
But their inquiries are being hampered by reports that another of the men they want to interview has left Ireland.
Investigators have now renewed their appeal to the public for help in solving the murder on January 16.
On Monday, mourners at Mr O'Connor's funeral heard how he was a big sports fan who was killed by something "wrong and evil".
Manchester United striker Wayne Rooney has expressed his condolences to Warren's family.
Garda Chief Supt Gerry Phillips has again appealed to anyone who may have been near the Grattan Wood apartment complex or the Hole in the Wall Road in Doneghmede, around 1am on the morning of the killing. "We are fairly satisfied we have identified all the people involved," said the senior garda.
"We have very good intelligence in relation to this and we now want to convert that into evidence."
Officers have already investigated 200 lines of inquiry and called at 200 houses as part of the evidence-gathering process.