Mandatory life sentences for murder in England and Wales and the system for setting minimum terms are unjust and outdated, a legal experts' group says.
The Homicide Review Advisory Group, made up of judges, academics and former QCs, says the system does not allow for sentences to match individual crimes.
The mandatory life sentence replaced the death penalty in 1965.
But Peter Neyroud, a former chief constable, said the public did not want killers treated with more leniency.
A Ministry of Justice spokesman said it had no plans to abolish the mandatory life sentence for murder. "The most serious crimes deserve the most serious sentences," he said.
The Homicide Review Advisory Group said a so-called mercy killing attracted the same mandatory life penalty as serial killings and it said it wanted sentencing for murder to be discretionary.
Its report builds on research last year which claims the public may support reforming the penalty for murder to make life imprisonment the maximum sentence rather than mandatory.
It claims that "with appropriate education" the public could develop "in the general direction long favoured by legal experts and the judiciary".
But Mr Neyroud, a former member of the sentencing guidelines council, said: "The public were very confused about murder sentencing and in fact regularly thought that the sentences for murder were too lenient, so I'm not sure that you can then leap to the conclusion that they're then ready for what would be quite a dramatic... and I suspect viewed as a reduction in seriousness."
The Homicide Review Advisory Group claim the mandatory life sentence was a compromise arrived at to ensure the abolition of the death penalty made its way through both Houses of Parliament.
It argues that the indefinite nature of a life sentence - which may or may not involve a life behind bars - is unfair and incomprehensible.
The starting point for a minimum term to be served for less serious murders is 15 years.
Offenders are released on life licence, which means they can be recalled to prison at any time during the rest of their life, if they breach the terms of their licence.
The report urges that the time has come for a move to fixed sentences for murder as with any other individual crime.
That would allow the exact circumstances of offences to be properly reflected by the courts, it says.
The Justice Secretary Ken Clarke recently announced plans to extend mandatory life sentences for many other crimes as part of a plan to do away with indeterminate sentences.