Baker Todd Mooney, 54, and his daughter Kirra, 10, were found dead after fire tore through a large shed at their home on Fenwicks Road in Biggenden about 12.20pm on December 20.
Police have released CCTV of two witnesses who police urgently want to speak to as part of their investigations.
The footage was taken at the Ban Ban Springs BP Service Station, on the corner of the Isis Highway and Burnett Highway at 12.20pm on December 20.
Police have said the man and woman, who were travelling together, are not linked to Mooney and his daughter.
Detectives are appealing to the pair, or anyone who recognises them or their car, to contact police immediately.
Police want to urgently speak to any motorists travelling along the Isis Highway between Goomeri and Biggenden or at the Ban Ban Springs BP Service Station between 11am and 1pm on December 20.
Mooney had been due to marry his long-term partner at his home last week.