Offenders on probation or community sentences could commit further serious crimes because the system is "not doing enough to learn from past mistakes", inspectors have warned.
Last year, 138 people in England and Wales were killed by offenders, who were back in the community and being monitored by probation services.
Last month, the National Probation Service apologised to the family of Nicholas Churton, murdered by an offender in north Wales who had recently been released from prison and was under supervision.
Jordan Davidson was freed in December 2016, after serving two and a half years for burglary and weapons offences.
He went on to murder Mr Churton, 67, in a machete and hammer attack at his home in Wrexham just three months later.
Davidson had breached his licence conditions on numerous occasions before Mr Churton's murder, but was never recalled to prison.
Her Majesty's Chief Inspector of Probation Justin Russell said authorities risked further tragedies in future, unless lessons were learnt.
A team of inspectors examined the way in which probation services carry out reviews and learn from serious crimes committed by offenders under their supervision in the community.
Mr Russell said there was a "lack of independent oversight and transparency" in the review process.
"Our inspections found that individual reviews were good in parts," he said.
But he added, more than one in five of those inspected "failed to give a clear judgement as to whether all reasonable steps had been taken to manage the risk of serious harm".
"At a national level, more needs to be done to identify trends and themes to drive changes to probation policies and guidance."
Around a quarter of a million people are currently on probation in England and Wales.
Just over 0.2% go on to commit other serious crimes, including murder, rape and serious violent offences.
The case of serial rapist Joesph McCann thrust the issue of poor community supervision into the national spotlight.
Authorities were warned as far back as 2011 that McCann was a serious risk, but missed eight opportunities to keep him behind bars.
After his release on an indeterminate sentence in February last year, he went on to commit a string of rapes and abductions in London, Luton and the North West.
One probation service case worker has since been demoted.
The Chief Inspector of Probation has made a series of recommendations around better management of the serious further offences (SFO) review process:
The family of Conner Marshall, 18, battled for five years for answers around probation failings, after the teenager was murdered by a repeat offender in south Wales.
In January, a coroner concluded that the private probation company involved was woefully inadequate in its oversight of the inexperienced probation officer, who had responsibility for supervising Conner's killer David Braddon.
The 25-year-old, who had a string of previous convictions, had been on probation after an assault on police and multiple drugs offences.
The company responsible for Braddon's supervision went into administration last year and its caseload has now been taken over by the National Probation Service.
The Ministry of Justice is currently involved in a process to end all of its contracts with privately owned Community Rehabilitation Companies across England and Wales.
Their areas of responsibility will all be taken over by the National Probation Service by June next year.
Responding to HM Chief Inspector of Probation's latest report, Conner Marshall's mother Nadine told Sky News: "I'm appalled at the on-going crisis within the probation service.
"It is still not learning lessons. It is continuing to put communities at serious risk of harm."
A Ministry of Justice spokesman said: "Serious further offences are rare but each one is scrutinised so that probation officers can improve the work they do to reduce the risk of others coming to serious harm.
"In most cases, reviews find errors by individuals, rather than systemic failings and action is taken to address them.
"However, where wider issues have been identified, the National Probation Service has acted to put them right."
The MOJ has agreed to allow inspectors to assess the reviews and new guidance and mandatory training is being provided.