Brother Dan Whalley said the Independent Office for Police Conduct (IOPC) had dismissed a complaint by 57-year-old Carl Whalley against officers in Chorley "without a valid explanation" when he was still alive.
And when the IOPC was asked to look at the matter again following Carl's death last October, relatives were shocked that the body responsible for police conduct handed it back to Lancashire Police to carry out an investigation into itself.
"For Lancashire Police to investigate themselves again is ludicrous," stormed brother Dan.
"I sent information to the IOPC which may have been relevant to the inquiry, but they simply advised me to send it to the police force who are being investigated.
"This is exactly what happened to Carl's complaint before it was dismissed."
Dan is set to give evidence at the full inquest into his brother's death at Preston on March 8.
The hearing has been scheduled to take two hours. But Dan says his statement - all 3,000 words of it - could fill that timescale on its own.
He told the Post: "The family are all disgusted with the way that the police conducted themselves before Carl was killed.
"He had already raised a valid complaint with the IOPC which was dismissed without a valid explanation.
"The reason this is so important is that the subject matter of Carl's complaint is still happening even after his death.
"As for the inquest only allotting two hours - my statement alone is 3,000 words and they have known this since January 20. It could take the entire two hours just to go through it."
Over the two years prior to his death Carl Whalley had complained to the Lancashire Post on a number of occasions about what he felt was a reluctance by officers to deal seriously with a long-running neighbour dispute.
And on the morning of his death he published a detailed series of allegations about the case on a website. Hours later his body was found in the rubble after a fireball destroyed his semi-detached dormer bungalow in Kirkby Avenue, Clayton-le-Woods.
A post mortem showed Carl had died from smoke inhalation and burns. A melted petrol can was found behind the front door of the property and traces of an accelerant were found on downstairs curtains.
The family say they alerted the IOPC to the website's content and their continued concerns that the matter was not being investigated thoroughly.
But after Lancashire Constabulary referred itself to the IOPC - normal procedure in cases where officers have spoken to someone shortly before their death - it was bounced back.
The police were asked to carry out a "local investigation" and put together a report about the actions of the force in responding to Mr Whalley's complaints.
In response to Dan's comments, an IOPC official told him: "As you are aware this matter is being locally investigated by Lancashire Professional Standards Department (PSD) as such I am unable to comment further on this case.
"However, I will advise that should you have any new information, you should forward this onto Lancashire PSD directly.
"Further to this, should you wish to make a complaint about the police you can do via Lancashire Constabulary’s website or via the IOPC website and we will forward this to the PSD."
Lancashire Police has been approached for a comment.