So much focus on the cars ... these second interviews must have been conducted just after the police finally got the forensic results from the cars. Maybe besides blood, they found cleaning fluid (the fluid used to clean up the blood) and they want to establish that cleaning fluid isn't normally stored in the back of the car?
There also seems to be a lot of focus on sickness in relation to all of them - would this only be in relation to the chemist visit or would there be another reason I wonder. Maybe GBC said something and the police are trying to catch him out - not sure.