It is sloppy... but at the time I guess the Police are pretty confident Sheila did it. They've already told Colin Caffell what has happened. JB is now hands on with family affairs/business (i.e. having access to office,vehicles, paperwork etc)... they probably have no reason to think anything is wrong..
example..
JB: Please burn all these things here that are a constant reminder of the horrific night at this house.
COP: Ermm sorry can't do that, its evidence.
JB: Evidence of what? you know who did it!
COP: Good point.. oh well, got any matches.
I'm not saying thats what happened...
