Police officers who failed to arrest Nottingham killer Valdo Calocane were allegedly told their disciplinary case had been "politically motivated" and would not result in severe punishment.
The Independent Office for Police Conduct (IOPC) has launched an inquiry into claims that some of its staff told officers the investigation was being "driven by the families".
They allegedly told officers from Leicestershire Police not to worry and reassured them they would only face "words of advice or reflective practice".
The IOPC launched an investigation into the officers last year, after it emerged that they had failed to arrest Calocane for a violent assault just weeks before he stabbed and killed 19-year-old students Barnaby Webber and Grace O'Malley-Kumar and 65-year-old school caretaker, Ian Coates.
Despite a warrant being out for Calocane's arrest at the time for a previous assault, officers allegedly did not attempt to arrest him or interview witnesses.
The IOPC identified 11 failings and advised that the officers face a misconduct hearing.
However, the process had to be restarted after the victim's families complained about "significant errors and vital omissions" in the investigation.
Officers behind the inquiry have complained about the handling of the first case, alleging IOPC staff told them they were effectively in the clear.
LATEST DEVELOPMENTS
- Nottingham attack survivors speak out for first time as victim says she wishes killer Valdo Calocane 'had taken me instead'
- Martin Daubney demands justice for Nottingham attack victims as he joins families on two-year anniversary: 'People need to held accountable!'
- 'Hold the authorities to account' Mother of Nottingham stabbing victim blasts system's 'failure' and vows' we will not go away'
University students Barnaby Webber and Grace O'Malley-Kumar were killed in the attack
|NOTTINGHAMSHIRE POLICE
The officers are understood to have claimed IOPC investigators told them the case against them was "politically motivated" and driven by the grieving families.
Families of the victims said the revelations raise questions about the "legitimacy, honesty and integrity" of the IOPC investigation.
In a statement, the families said: "The scale of failures that we have already endured at the hands of the institutions and organisations that contributed to the entirely preventable deaths of Grace, Barney and Ian are shameful.
"To now be made aware that the IOPC, the very body that alleges to independently hold our police force to account, may itself be complicit in such gross misconduct, is terrifying."
The statement continued: "This development not only puts into question the legitimacy, honesty and integrity of our own investigations, but also to those taking place on a national level."
The families said that if they cannot trust the IOPC to hold the police accountable, "who can we trust?"
An IOPC spokesman said: "We are aware of allegations made about IOPC staff by Leicestershire police officers who are subjects of an IOPC investigation.
"The allegations involved comments alleged to have been made about that investigation.
The IOPC identified 11 failings in arresting Calocane
| PA"We are treating this matter extremely seriously and have commissioned an external party to investigate them alongside other complaints about the investigation made by the families of the victims.
"We will continue to provide the families with regular updates as these matters progress."
It is understood that the staff who allegedly made the comments are no longer working on the case.