The daughter of one of Shipman's victims welcomed the two reports into the investigation of the serial killer, saying she hoped it would lead to a more open and accountable health system.
Dr Shipman told paramedics he had given Mrs Overton morphine
Shipman was called out to Renate Overton, 47, at her home in Hyde, Greater Manchester, in February 1994 by her daughter, Sharon Carington, who feared she was having an asthma attack.
Shipman gave Mrs Overton a nebuliser, but while her daughter was out of the room it is believed he also injected her with morphine.
She slipped into a coma and died more than a year later.
The death was never investigated further, despite Shipman telling paramedics he had given her morphine.
Dame Janet Smith, the judge appointed to study the case of the Manchester GP, has criticised the initial police investigation into his killings, and called for a reform of the coroners' system.
Sharon Carrington, who lives in Hyde, said: "We will never understand why those responsible for my mother's care didn't see fit to report Shipman's treatment.
"Had they followed this up we believe it could have prevented many more deaths at Shipman's hands.
"What we hope now is that our mother's death wasn't in vain and that any recommendations made for change will be implemented.
"We hope that this will lead particularly towards a more open and accountable health system where medical professionals can feel free to raise their concerns without fear, and that all concerns and complaints which are raised will be investigated."
Mrs Carrington said the family were still coming to terms with the way her mother died.
She added: "The events on the day that my mother first fell ill happened so quickly we
were left in a state of shock and extremely distressed.
"I remember that shortly after my mother's admission to hospital something was mentioned to our family about Dr Shipman having administered morphine to my
"However, at such a distressing and shocking time we didn't understand or take in what was being said."
The coroner who reported Harold Shipman to police, John Pollard, said that he accepted that the police investigation "did not obtain the results it should have".
He said: "The saddest thing of all is that three people died because that investigation failed to lead to the arrest of Shipman."
Mr Pollard welcomed the call for an overhaul of the coroner system, saying he hoped that it would stop anything like the Shipman case happening again.
But he added: "One can never say never in these circumstances.
"A determined murderer, particularly one as plausible as Shipman, will always be difficult to detect."
James Purnell, Labour MP for Stalybridge and Hyde, said: "Today's report shows once again that the victims' families were right to push for a public inquiry.
"The findings about the failures of the police investigation will be distressing to all those relatives concerned."