First post- been watching comments for days and some interesting comments! Also a Brissy girl O's so hard to get decent news.
Not familiar with area, but how close are the show grounds in relation to the screams heard by neighbours? Perhaps A threatened to leave with children, fight ensued, she drives off, goes to show ground to call for help. G ph's mistress in a state, then follows. Possibly drags her into his car (scratches on him from altercation), something happens, he dumps body over bridge, goes to parents house to dispose of clothing. Just ideas, but could explain re-interviewing of mistress to determine times etc and his state of mind.