There were two key witnesses in the Robert Farquharson case.

The first was Greg King, an old friend of Farquharson, and the story he told provided police with something they desperately wanted for their case - a motive for murder.

The other witness, Dawn Waite, came forward four years after the crash. She said she had actually seen Robert Farquharson on the night of the crash, as he was sizing up his exit from the road.

But how reliable are they? And how much can we trust our memories?

For exclusive content and additional reporting on the case, available to subscribers of The Age and The Sydney Morning Herald, visit theage.com.au/trialbywater or smh.com.au/trialbywater.  Subscribe now to access the special Good Weekend investigation, which features never-before-seen 3D models recreating key scientific evidence, video, audio and other interviews.