it’s weird but I am of a similar thought. The murder did happen just after picking the girl up…this is mostly established now. He left no signs of a struggle, no blood splatter, no dna and no trace.
that suggests to me it was possibly strangulation with a ligature or something quick and surprising.
in terms of disposal, it was day time and there’s a risk of being spotted. He didn’t have long and spent 9 minutes on the phone to the mother.
I think he’s just dumped the body somewhere. Not so much pigs, but we have foxes, badgers, crows and (in the dykes) pikes and eels. Between them they can make quick work if no one is looking.
Remember she wasn’t reported as missing for 4 days and the police didn’t do a proper search for three months! All this during lockdown too