Prosecutors have been ordered to look again at possible manslaughter charges after a teenage roofer fell to his death in his first week at work.
Daniel Dennis, 17 from Pyle, Bridgend, died after falling through a skylight at a store in Cwmbran in 2003.
The Crown Prosecution Service (CPS) decided a criminal prosecution against a firm would not succeed despite an inquest verdict of unlawful killing.
A High Court judge has ruled the matter should referred back to the CPS.
Daniel had been working for just seven days in his first real job for roofing company North-Eastern Roofing when he was killed at Matalan in April 2003.
This is a landmark ruling as it's only the second case where the courts have interfered in a work place death.
His father Peter took legal action, through the GMB trade union, asking the High Court to quash the CPS's decision not to bring a prosecution for gross negligence manslaughter.
Giving his ruling on Friday, Lord Justice Waller said there were "failures" over factors which influenced the CPS not to prosecute.
The judge said a solicitor acting for the CPS did not take into account the "seriousness of a failure to give proper instruction not to go on the roof prior to induction or proper instruction".
He also said the CPS had not taken sufficient account of the Newport inquest jury's unlawful killing verdict in March last year.
Daniel had gone onto the roof of the store looking for a piece of timber for a colleague when he fell through a skylight.
He landed on the shop floor, suffering severe head injuries and internal bleeding and later died in hospital.
The court said the matter should be referred back to the CPS and that it was possible that a different decision could be made when these factors are taken into consideration.
But the judge said the final decision still rests with the CPS.
After the ruling Peter Dennis said: "This decision gives us some hope this new year that justice for Daniel will finally be achieved."
Mick Antoniw, one of the solicitor's acting for the Mr Dennis, said: "This is a landmark ruling as it's only the second case where the courts have interfered in a workplace death. "We now expect the CPS to review and overhaul the way they consider the evidence in cases involving workplace deaths."
The CPS said it would not comment on the case until it had seen a copy of the court judgement.