It’s easy to theorise how Cannan, having been caught almost red handed in ‘81 (he was always a fairly sloppy offender), spends his days inside ruminating on his misfortune and hatching a plan to make sure that won’t happen again. Would he have wanted some sort of accomplice? Probably not in my view, but maybe all the pretty yuppie women kicking about London in late spring, early summer ‘86 were too much for him to resist, he needs a property in which he won’t be disturbed and that’s where his pal comes in - WL covers this well. He sees the for sale sign at 37SR - which as WL has explained isn’t far from his pal’s place - and calls Sturgis, arranges a viewing and decides to abduct whatever female agent turns up. And the rest as they say is history. He tries repeating the trick in Bristol in ‘87 with Shirley Banks, but without an accomplice to keep him right his typical sloppiness ultimately proves his undoing.
I’m not so convinced that police could’ve nailed him in ‘86 though. Cannan can say he’s up in Birmingham and his mum will back him up. So now what? It was a simpler time and considerably harder to prove when people were lying about their movements. If they say he’s a rapist ergo he must be a liar then the same must be true for all the other rapists, perverts and weirdos without watertight alibis who would’ve been knocking about Fulham that summer. Tracing all their associates in a bid to corroborate their movements would be an arduous task too, and of course these associates - like Cannan’s pal - would also likely be criminals of some sort, so everything they say must be viewed with skepticism also. It’s easy to see how such an investigation would become bogged down and lose its focus.