The allegations of an inappropriate relationship between Laniet and Robin Bain cannot be substantiated.  They are based on hearsay.  The testimony was initially provided by a Dean Cottle whom the judge in the first trial deemed to be unreliable.  Dean Cottle was subpoenaed to turn up at both the original trial and the retrial and both times failed to turn up.  In the end his affidavit was read out by the judge in the retrial, an occurrence that has been questioned on two fronts a) since the witness did not turn up his testimony could not be tested and b) the judge reading it gave it more weight than it might otherwise had if read out by a court clerk.

The testimony was further corroborated by a prostitute and a dairy owner, both who made similar statements in the retrial of 2009.  Many have argued that Laniet was disturbed and was also telling stories about becoming pregnant and having babies, both of which have not been substantiated.  In light of that, Laniet can be considered an unreliable witness herself and may have been saying things just to attract attention.  It is well known from McNeish's account of the Bain family that Robin and Margaret had rather overt sexual behaviour in their earlier years which might have contributed to a certain openness about sexual matters from the children and certainly greater awareness of it than the norm.  If Robin was conducting illicit affairs with his daughter it seems unusual that she should choose to give up her independent flatting arrangement to go and live with her father at the schoolhouse prior to the murders.  The other person who lived with them, Kyle Cunningham boarded for up to four months with the pair. According to a report in the herald:

Under cross-examination by Crown prosecutor Cameron Mander, Mr Cunningham said Robin "seemed as normal as Robin Bain was any day of the week" on the Friday before the killings.

He said Robin and Laniet appeared to have a normal father and daughter relationship.

Mr Cunningham also confirmed that Robin helped him move into the Taieri Beach School house.

This testimony counters any idea that there was incest happening.  Laniet was 17 at the time and at that age is very unlikely to voluntarily live with an abuser when there were other alternatives.  On the contrary, for every story suggesting incest, there is another story suggesting that Laniet was scared of David Bain and he was the reason that she left school and then left home.  This includes stories of David threatening family members with his gun and planning to commit an criminal act while using the paper run as an alibi.