Kent police commissioner Ann Barnes voiced "very deep concerns" about the government's plans, which are due to start in October.
The changes will mean families of people murdered before 2010 will no longer get specialist help to deal with their loss and trauma.
However, the Ministry of Justice has said, Mrs Barnes could fund the service herself.
The changes would mean a lack of support in preparing for an inquest and a potential court trial through to counselling.
The money comes from a national pot that can be distributed according to local need.
Mrs Barnes said: "Hundreds of families in England and Wales are currently receiving coordinated and specialist support.
"Given the funding is aimed at a small, specifically vulnerable group, it seems churlish to remove it.
"What it says to me is that families bereaved before 2010 don't count: it is an announcement made without a scintilla of common sense, humanity or consideration to the families.
"Murder brings violence and extreme trauma to law-abiding families, who become, as a result, victims of crime in their own right. As a nation we should recognise this and offer whatever support it takes for loved ones to deal with their loss.
"I am very much against a 'one size fits all' approach, except in this case, because the needs of those who have lost a family member to murder are complex and unique."
She added: "Kent has had significant success in cold case reviews.
"Thanks to major advances in forensics more and more historic murder cases are being solved.
"What can we possibly say to families who finally get answers many years after their original bereavement?
"That their case is not as important or valuable as one that happens after 2010? I am afraid this is a logical conclusion."
From October, PCCs will be responsible for commissioning the majority of victims' services in their areas, including support for those bereaved by homicide pre-2010.
Policing Minister Damian Green has responded to Mrs Barnes saying the issue around funding will be urgently looked at.
He said: "I am urgently looking at how we best ensure support for those bereaved pre-2010 continues.
"I will make sure no one is disadvantaged by the move to the new funding model for victims’ services.
"Losing a loved one to homicide is devastating and it’s vital that there is specialist help and support available, no matter when the crime was committed.
"We currently provide £2.4 million each year for a dedicated, national homicide service, as well as funding a number of charities providing specialist support.”
An MoJ spokesman said: "It's a change in the funding model rather than a cut - we are actually looking to double the overall funding to support victims of crime with PCCs getting the majority of this for local victims' commissioning."
Mrs Barnes added: "This shows the power of Police and Crime Commissioners - we are here to represent the local people and to stand up for their rights.
"My colleagues and I have been up in arms about this decision as victims should be at the heart of the Criminal Justice System.
"For me, it was an absolute disgrace to consider taking funding and support away from bereaved families – it’s grossly unfair.
"This is an issue that has touched the hearts of the public and I’m pleased that I have been able to react to local needs and helped to push this onto the Government’s agenda."
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