Thanks for informing us about Peter Hyatt, Tortoise. I've watched several of the youtube videos and been very interested, though I do find him a bit slow and repetitive. I thought most of his points with reference to the 911 call and radio interview he was discussing were valid and could see many parallels with IS.
I'd be wary of accepting a statement like 'a science that never fails', though, partly because he's selling his own business and partly because it's clearly not a science but a skill based on experience of how people behave. I couldn't help my hackles rising when he made statements like 'Pronouns predate language' - they don't, obviously. (It also struck me that cultural norms on pronouns are quite variable. I lived for years in a society in West Africa where it was frowned upon for a parent to refer to or address the eldest son, or a wife to refer to or address her husband, by name - they'd be in deep trouble if they ever rang 911 in the USA and Peter Hyatt were to analyse the call!)
I expect you know about forensic linguistics in this country? Jan Svartvik on the Evans case in the late 1960s, Malcolm Coulthard on Derek Bentley and others (too late, often, but still). But I think their work was mainly on identifying authorship rather than guilt. I'm probably completely out of date. Aston University is strong in this area but I don't know how much their work is used by courts.