The pair said they told police about the unusual sighting at the time - but police told the Herald they had no record of it.
Police had undertaken an "extensive search of available documentation" but had not been able to locate or identify any material relating to the pair's version of events, according to a police spokeswoman.
Their sighting could be significant as it raises uncertainty around whether David Bain was home when the family computer was turned on, Stuff reported.
The defence argues Robin Bain shot his family and turned the computer on before turning the gun on himself.
While the Crown argued Bain had time to turn it on once he finished his paper run and write: "Sorry you are the only one who deserved to stay".
Earlier witness accounts claimed Bain was standing outside the gate of his home at 65 Every St between 6.40am and 6.45am.
However the latest evidence puts him outside the house at 7am - just nine minutes before he made the call.
Bain has also struggled to recall, claiming to have gone into shock, about what happened in the 25 minutes from him arriving home and calling police at 7.09am.
Wilson and McLellan claim they both tried to contact the Bain defence team with their accounts after the 1996 trial, but never heard back. They were also never asked to give evidence at the first trial.