Detectives investigating the murders of a mother and her young daughter have made a major breakthrough in their inquiries identifying a key suspect in the killings. 

Police in NSW and South Australia have been inundated with information and tip-offs from the public a day after they went public with the identities of single mother Karlie Pearce-Stevenson and her daughter Khandalyce Pearce-Stevenson.

Fairfax Media has learnt that investigators in both states have made rapid progress in the investigation and have identified a male suspect.

It is understood the man is in custody in a NSW jail, serving a prison sentence for unrelated offences.

A spokesman on Thursday night said police were "keeping an open mind" to their inquiries.

"Police are following a number of lines of inquiries in relation to the deaths of Karlie and Khandalyce Pearce-Stevenson," the police spokesman said.

The revelation came 24 hours after they revealed that the body of a woman dumped in Belanglo State Forest that was discovered by trial bike riders in 2010 was single mother Karlie Pearce-Stevenson. 

Investigators said that she was the mother of Khandalyce Pearce-Stevenson, whose body was found in a suitcase in July off the Karoonda Highway, near the South Australian town of Wynarka.

Police only learnt the identities of both victims in the last fortnight and that both homicide cases were related. The breakthrough came via a tip-off to CrimeStoppers on October 8. 

Their deaths are now the subject of a joint murder investigation by SA and NSW police and also involving their counterparts in the ACT and NT.

South Australian police said on Thursday they had received 30 CrimeStoppers calls relating to Ms Pearce-Stevenson and her daughter. 

Dozens of calls have been received by police in other states, including NSW. 

The last known sighting of Khandalyce and her mother was on 8 November 2008, when they were stopped by police while driving down the Stuart Highway near Coober Pedy in South Australia.

At that time, Karlie was aged 20, and Khandalyce was aged two.

Ms Pearce-Stevenson went through primary school in Braitling in Alice Springs' northern suburbs, where she also spent part of her childhood. 

The keen netball player went to Alice Springs High School before leaving the Northern Territory town after 2006 with Khandalyce. 

A man who knew Ms Stevenson-Pearce as a teenager said she was a nice girl who met a horrific end. 

The man, who did not want to be named, said he knew her and a close friend from parties when they were younger.

"I know she had her kid and then her and Andrew (the child's father) had troubled times," he said.

He said he didn't know she had been missing until police revealed the breakthrough on Wednesday. 

"That's why the story shocked me yesterday," he said.

Ms Pearce-Stevenson's step-brother, Luke Povey, still lives in Alice Springs and works as a glazier. 

Her step-father is also to believed to live in the town, along with extended relatives.  

Her mother Colleen Povey died in 2012.

Police said Ms Pearce-Stevenson's extended family had believed mother and daughter had been living interstate alive and well.

The family has appealed for donations to assist with the costs of repatriating their bodies back to Alice Springs. 

According to the crowd-funding page, believed to be organised by Ms Pearce-Stevenson's cousin, the family "spent the last six years desperately trying to locate their whereabouts" after the pair went missing in 2009.

"Our family is asking for assistance to help us raise the funds to bring Karlie and Khandalyce's remains home to Alice Springs so that they can be reunited and laid to rest together with family."

In 24 hours, the family raised $5000 from more than 40 separate donations.

It was call 1267 and then 1271 to Crime Stoppers that provided the key breakthrough to two baffling murder investigations running in two separate states.

Homicide detectives in NSW had exhausted almost every avenue in the past five years trying to identify a young woman whose remains were uncovered in the Belanglo State Forest, south of Sydney, in August 2010.

South Australian police had worked tirelessly without any luck since July to discover who the young girl was whose body was found dumped with clothing and a quilt in a suitcase in bushland off the Karoonda Highway near Wynarka.

Then, on October 8, the first call came through that not only provided a breakthrough but linked the two investigations in the most tragic way.

The caller outlined that single mother Karlie Jade Pearce-Stevenson and her daughter Khandalyce had been missing for six years.

"The initial caller identified that Karlie and Khandalyce had been missing since about 2009, although at the time of the call there wasn't a missing person report in existence," South Australia Police Detective Superintendent Des Bray said.

That call was the 1267th received by South Australian detectives in relation to the Wynarka investigation.

Four calls later, someone provided a photograph showing Khandalyce in a stroller with the quilt that was found in the suitcase with her bones. Then a later photograph showed Khandalyce wearing a pink dress found in the suitcase.

"As a result of that we were able to progress a lot of work around government records and were quickly able to ascertain that Khandalyce had her immunisation but after that there were no records and she was never enrolled in school," Superintendent Bray said.

Police were able to gain access to Khandalyce's medical records and matched a previous blood sample with DNA from the bones found in the suitcase.

The investigation then turned to Khandalyce's mother, Ms Pearce-Stevenson, who left the Northern Territory with her child between 2006 and 2008.

Investigators contacted homicide detectives in NSW and the focus turned to the case of a young woman whose bones were discovered in the Belanglo State Forest in 2010.

She had been known as "Angel" due to the "angelic" motif on the T-shirt that was found with her remains.

DNA from those bones, which were sitting unidentified in a box in the Glebe Morgue, were cross-matched to the bones found at Wynarka.

By Friday night last week, police had confirmed Angel was in fact Ms Pearce-Stevenson, Khandalyce's mother.

It was the breakthrough two strike forces in two states had been waiting for.

"This is one of the most shocking crimes, shocking and unimaginable and another family has been torn apart and devastated," Superintendent Bray said.

"Those people that are responsible for this crime are truly evil and must be quickly caught and held to account for what they've done."

Police sources have confirmed that, as of a month ago, detectives on either case had not even compared notes on the investigations or looked at possible links.

Ms Pearce-Stevenson's mother had reported her daughter missing to Northern Territory police on September 4, 2009 but she withdrew the report six days later after receiving information that Ms Pearce-Stevenson was "alive and well", police said.

It is understood the mother had received a text message or a phone call telling her that her daughter was fine but did not want any further communication with her.

However, investigators aren't certain whether it was Ms Pearce-Stevenson or someone else who made the call or sent the message.

Even after 2009, her family believed the mother and daughter were living safe and well interstate.

Ms Pearce-Stevenson's mother died from an illness in 2010.

Before their breakthrough, police had been painstakingly going through names drawn from searches of government databases, including immunisation and Centrelink.

In the Wynarka case, if a child got to a certain age and stopped appearing on records, her name might have made the list.

Now police have the names and have compared them against some government databases, it appears the mother and daughter were "completely off the grid".

The last reported sighting of the pair was on November 8, 2008. Ms Pearce-Stevenson was seen driving a car with Khandalyce on the Stuart Highway near Coober Pedy in South Australia.

At the time Ms Pearce-Stevenson was aged 20 and Khandalyce was two.

"It's absolutely baffling," head of the NSW Homicide Squad Detective Superintendent Michael Willing said.

"Here we have a young mum and a little girl who decide to leave the Northern Territory for whatever reason ... and travel around Australia and then their remains are discovered years later.

"It's a complete mystery to us."

Detectives have numerous lines of inquiry but would not say if they had a suspect. All they would say was that both mother and daughter suffered violent deaths and that family members have been ruled out as suspects, including the child's father who, it is understood, still lives in Alice Springs.

The pair at different times had visited friends in Darwin, Alice Springs, Adelaide and Canberra and investigators wanted anyone who might have seen mother and daughter at motels or caravan parks between 2006 and 2008 to come forward.

A joint agency operation involving homicide detectives in South Australia, NSW, the Northern Territory and ACT has now been established to investigate both deaths.