More than four decades after one of New Zealand's most notorious double killings, a website has been launched to try and help solve the murders of Jeanette and Harvey Crewe.

The website www.crewemurders.com, set up by researcher Chris Burt, hopes to elicit even more information on the mysterious killings, at rural Pukekawa, south of Auckland, in June 1970.

The Crewe's 18-month-old daughter Rochelle was left at the house - looked after by an as yet unidentified woman for five days before the murders were discovered.

Neighbour Arthur Allan Thomas was twice tried and convicted of the murders, but pardoned and freed in 1979 when it was revealed police had planted a cartridge case in a garden to frame him.

Birt has reported on the murders since 1976 and in 2001 produced a book, The Final Chapter, which named Jeanette Crewe's father, Len Demler, as the killer. Demler died in 1992.

The website provides a raft of information available on the case, and also provides a "conduit" for witnesses.

Birt told Fairfax he hoped the site would provide the breakthrough sought by Rochelle Crewe and the Thomas family.

"I will work with any witnesses. Ill check it out as best I can, and with their approval, take it to the authorities."

Detective Superintendent Andrew Lovelock, who is leading an internal police review of the case, also called on anyone with information to come forward, as it could be their last chance.

The review of the case was launched in 2010.

"I would be surprised if this exercise will ever happen again. If people want something considered, and there's been something on their mind for years, now is the time to advance it, frankly."