zane gbangbola died at home in the middle of the night after gas poisoning .
authorities denied that deadly fumes were coming from nearby landfill site .
they insisted carbon monoxide from faulty pump in house caused his death .
evidence shows authorities knew hydrogen cyanide leaked into family home .
fire crews fled the riverside home for their own safety after their specialist gas detectors sounded the alarm for dangerous levels of hydrogen cyanide four hours after zane was discovered by his mother .
the concentration of the gas found could be fatal within 15 minutes ; .
carbon monoxide was never detected in the family 's home ; .
neighbours were evacuated amid fears of ` contamination from floodwater ' ; .
police and other agencies were fully informed of hydrogen cyanide at the property at the time , but never confirmed it publicly despite repeated questioning by this newspaper .