The mother Rebecca Goden has written to Swindon killer Christopher Halliwell urging him to confess to her daughter's murder.
Karen Edwards told ITV West that her daughter was last seen alive by her family a decade ago.
His daughter Natasha Halliwell has also urged her father "to do the right thing."
The murder trial into the death of Sian O'Callaghan has ended, with the life imprisonment of her killer - taxi driver Christopher Halliwell.
Wiltshire Police have made a statement following the jailing for life of Christopher Halliwell for the murder of Sian O'Callaghan.