The 19-year-old was reported missing on June 19, after she failed to return home to Kingsvale, where she lived with her six-month-old son and a married couple.
During early enquiries, police were told that the couple had dropped Ms Haigh off at Campbelltown train station.
An inquest in 2011 found Ms Haigh likely died by murder or misadventure, however the case was reviewed by the Homicide Squad in 2020.
Then last week as police increased the reward for information about Ms Haigh's disappearance to $1 million, strike force detectives seized a white Suzuki Sierra from Thurgoona, near Albury last Wednesday for further forensic examination.
Today, NSW Police Homicide Squad detectives made an extraordinary breakthrough, arresting a married couple at a property in the Riverina region.
The man and woman, both aged 61, are expected to be charged with murder.
Police will provide an update this afternoon.
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