Imagine if someone discovered the killing, and was about to phone the police, when David pushed them, and accidently killed them. From then on, the Platts get more and more disturbed, and the stress causes them to actually kill some more.

Over a period of say 10 years they get darker and darker, sneaking out to the red wreck in the darkness of night looking for another victim.

Who would their victims be and how would they kill?

I think Marion Logan and Gemma will be likely candidates for the murder. Marion will more than likely get the truth out of Kylie and try and phone the police and Kylie will kill her out of desperation.