The father of murder victim Donna Cleary has demanded an explanation from the Director of Public Prosecutions (DPP) as to why no-one has been charged in connection with her killing – and has said he will go to the European Court of Human Rights if the DPP fails to respond.

The 22-year-old mother-of-one from Coolock was shot dead at a house party on 5 March 2006. Her parents Peter and Kathleen and her son Clayton (5) will mark the three-year anniversary of her death privately on Thursday.

The main suspect in the case, Dwayne Foster, died from a brain haemorrhage in a garda cell after being questioned about his role in the young mother's murder. Three other men were in the company of Foster when the shooting took place. It is understood two of these men are in prison for "a latitude of other offences" while the third man is living in the UK after recently being released from prison.

DPP James Hamilton announced in October last that his office would give reasons for not prosecuting, or not proceeding with a prosecution, in cases where a crime had resulted in a death. This policy change applied to all cases that resulted in death since October 2008.

Peter Cleary said: "I cannot understand why the DPP didn't charge the three others with their involvement. I will be demanding an explanation from his office.

"We're talking about murder here. These people should be held accountable, they have been identified as being involved."

Following the death of Foster, the DPP directed that no prosecutions be brought against the three other men.

The young mother was killed when a man opened fire indiscriminately on a group of people attending a 40th birthday party at an address at Adare Green, Coolock. She died after being shot in the chest. The group of men had earlier been refused entry to the party.

A garda involved in the investigation said: "New evidence is required to bring the case forward but it remains open and has been extensive. There is still potential for prosecutions but we would need more witnesses or evidence."

Cleary said some of the witnesses to his daughter's killing were initially too afraid to give evidence against those involved but gardaí should re-interview all witnesses and offer them protection if necessary. "I will go to the European Court of Human Rights if I don't get answers from the DPP. It looks like I'm fighting a losing battle here. There were no witnesses to Rachel O'Reilly's murder but her husband got convicted over that."

In January last year, a 24-year-old woman was arrested on suspicion of possessing a firearm linked to the killing but was later released without charge. The DPP is currently considering a file in relation to her involvement but garda sources say it is unlikely the woman will face charges.