The berries and cream

This is one of the crime scene photos, which shows what looks like the remnants of berries and cream in glasses. Doesn't this kind of undermine the brothers words about the final argument? Of course, the parents could've eaten this beforehand, but it's still a possibility that they were eating or had just finished eating when this argument allegedly took place.

All of that said, though, if you were going to make up a final confrontation, wouldn't it be more dramatic and physical, with a clear threat? Plus, if they had been eating at the time, I'm sure the glasses wouldn't have ended up neatly placed onto the table.