Romeo Oscar Golf,
Why waste further time?
Because the role of the Police isn't just to generate facts to fit the case but to investigate. This means covering all possible scenarios, scrutinising motive, examining backgrounds. The forensics themselves take hours if not days to gather.
I agree, in an apparently clear cut case such as this it seems OTT but who would want to be the Senior Investigating Officer in a case that was thrown out because some i hadn't been dotted?