Has it ever been revealed what type of cocaine metabolites were present in the hair sample, or is it nondescript? Can someone provide a link to whatever report is available? Without showing my hand, I have some expertise in this field.
Cocaine has at least 1 metabolite that can feasibly spontaneously hydrolyze in the presence of water (primarily the benzoyl metabolite). Other cocaine metabolite pathways necessitate some kind of enzymatic process to form.
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The benzoyl metabolite wouldn't likely be formed in any meaningful quantities in regular water however, and the formation would likely be a very slow process.
ALTERNATIVELY, the benzoyl metabolite can be formed in large quantities by alkaline hydrolysis, such as could be encountered from freebasing.
So in short, without further information, I would expect that either cocaine was ingested or there was exposure (by physical contact or otherwise) to crack, which is degenerate and pathetic on an entirely different level.