OFFICIALS missed a crucial opportunity to finally take toxicology samples from triple killer Valdo Calocane — by letting him have a haircut.
The monster got an indefinite secure hospital order after admitting manslaughter over his Nottingham knife rampage.
But The Sun revealed he refused to give blood and urine — which would have shown if he had taken drugs and possibly led to murder convictions.
It has now emerged officials allowed Calocane to have his hair cut, even though they could have extracted samples from it.
Hair retains tell-tale traces of substances, including recreational drugs, for years — with accuracy about when it was in the body.
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A source said: “It’s incredible really, after all the failings and all the issues raised by the families, they have made a mistake so basic.
"Hair samples could’ve been crucial for showing Calocane was under the influence of drugs at the time of the attacks.
“If that can be proved, it smashes his right to the lesser manslaughter plea and he is left facing the murder charges the families want him tried over.”
Calocane, 32, visited London to go to a party a day before killing students Barnaby Webber and Grace O'Malley-Kumar, both 19, and Ian Coates, 65, last June.
The Sentencing Council’s punishment guidelines for manslaughter by diminished responsibility state: “The degree to which the offender's actions . . . contributed to the seriousness of the mental disorder at the time of the offence may be a relevant consideration.
“For example: where an offender exacerbates the mental disorder by voluntarily abusing drugs or alcohol . . . ”
Nottinghamshire Police said Calocane did not have his hair cut while in its custody.
