Ministers have been urged to rethink proposals to reform the way deaths are certified and investigated to avoid a repeat of the Harold Shipman scandal.
Harold Shipman evaded the system for 25 years
A committee of MPs says plans in 2004 went some way to creating a system in England and Wales which could stop doctors from covering up crimes.
But the draft Coroners Reform Bill had dropped some of those reforms, the constitutional affairs committee said.
Constitutional Affairs Minister Harriet Harman also came in for criticism.
The draft bill includes proposals to shake-up the coroners' system in England and Wales and would allow coroners to ban the media from naming a dead person or publishing information that revealed his or her identity.
But the dropping of earlier plans to reform the death certification system, by ensuring that all death certificates were looked at by a medical examiner in the coroner's office, meant that loopholes would still exist, the MPs said.
The all-party committee added: "It is disappointing that the government has retreated from its 2004 proposals, leaving out much of what was good."
The MPs suggested that what was left of the plans merely tinkered at the edge of a system which had "critical defects", and the government risked wasting a "golden opportunity" to improve the set-up.
Ms Harman was also criticised for giving "unclear evidence" to the committee.
In particular, her assertion that the package was a "good set of proposals" was also contradicted by MPs, who said: "The evidence we have received is overwhelmingly to the contrary."
Dame Janet Smith, the senior judge who investigated the Shipman killings, told the MPs that the reforms contained in the bill meant "there could still be a Shipman out there killing patients".
The MPs urged ministers to reintroduce reform of death certification and ensure coroners were given sufficient resources and support to do the job.
Committee chairman Alan Beith said: "The system of coroners and death certification is in urgent need of reform on at least two counts - there is enormous variation of standards and the system failed to detect a major serial murderer.
"This is therefore an opportunity not to be wasted.
"We must strongly recommend that the government rethink its plans and that it incorporate reform of death certification.
"Attempting to reform the system without reforming the way it is funded is likely to prove a failure."
But a Department for Constitutional Affairs spokesman said proposals that all deaths - over 500,000 a year in England and Wales - should be subject to additional, independent medical scrutiny by the coroner service would be costly and "mean unnecessary delay and bureaucracy for bereaved people and professionals involved".
"We will continue to explore what changes to death certification can be made to complement these improvements," he said
George Fernie, chairman of the British Medical Association's forensic medicine committee, said the government risked missing "the opportunity of a lifetime to deliver a much-needed overhaul of our outdated system of death certification".
Dr Harold Shipman was jailed for life in 2000 for murdering 15 patients while a GP at Hyde, Greater Manchester. He hanged himself at Wakefield Prison in January 2004.
Dame Janet's inquiry concluded he killed at least 215 patients between 1975 and 1998, making him the UK's worst serial killer.
A further report recommended that all deaths should be reported to the coroner for examination.