Detectives investigating the disappearance of Sydney dentist Preethi Reddy spoke to her ex-boyfriend Harsh Narde before he died in a fiery car crash on the New England Highway.

Key points: Preethi Reddy was stabbed numerous times and dumped in a suitcase in Sydney

Preethi Reddy was stabbed numerous times and dumped in a suitcase in Sydney Police interviewed her ex-boyfriend Harsh Narde as part of their investigations

Police interviewed her ex-boyfriend Harsh Narde as part of their investigations He is also dead, after a fiery car crash on Monday night in regional NSW

Dr Reddy, 32, was found dead in a suitcase in Sydney's east on Tuesday night after she went missing on Sunday morning.

Dr Narde, also a dentist, was killed at Willow Tree — about 340 kilometres from where Dr Reddy was found — on Monday night in a head-on crash believed to have been a deliberate act.

Police confirmed they spoke to Dr Narde before his death.

The ABC understands he was the key suspect in Dr Reddy's murder.

The suspect died in a deliberate crash involving a car and a truck. ( Supplied: NSW Rural Fire Service )

NSW Police said the investigation was still in its early stages.

"I cannot qualify exactly what has happened and I won't put it out there because if we're wrong and it's not substantiated then we're doing a disservice to Preethi and her family," Detective Superintendent Gavin Dengate said.

"At this stage we know they met up in Sydney and now we're looking at all the movements between these two."

Pair met up on Sunday

Dr Reddy, 32, was attending a dental conference in St Leonards at the weekend, where the ABC understands she met with Dr Narde.

On Sunday, she told her family on the phone about 11:00am that she would head home after a late breakfast, and when she failed to return, relatives contacted police.

Through their own inquiries, officers found her body just before 9:30pm on Tuesday in a suitcase inside her grey Volkswagen Golf, which was parked on Strachan Lane in Kingsford, in Sydney's eastern suburbs.

Dr Harsh Narde died in a car crash at Willow Tree. ( Facebook: Supplied )

NSW Police said Dr Reddy was stabbed numerous times.

The last images police have of Dr Reddy show her at McDonald's on George Street in Sydney's CBD at around 2:15am on Sunday.

It was just hours after the Sydney Mardi Gras parade finished, and Dr Reddy was lining up in the restaurant alone.

She bought two bottles of water before leaving, walking south towards Market Street, where police said Dr Reddy was staying at a hotel with a man known to her.

Dentist Preethi Reddy at Woolloomooloo, in central Sydney. ( Supplied: Facebook )

Kingsford resident Fatima said police asked her about the vehicle that Dr Reddy was found in.

"They just asked about our details and then asked some questions about the car, so we have heard of something strange about the car, some chatters, some people," she said.

"It used to be a safe area so I'm just a bit concerned now.

"I told them I might notice the car before … I didn't notice anything strange about that."

'See you next week'

Dr Reddy worked at Glenbrook Dental Surgery in the Blue Mountains, about 70km west of Sydney.

On Wednesday morning her colleagues posted on Facebook about her death.

"Glenbrook Dental Surgery staff are in mourning to hear the sad news about Preethi Reddy," the post read.

Colleagues told the ABC they had been unable to sleep since her disappearance and patients had offered to help with the search.

"It's devastating, and this is completely out of character," dental assistant Chelsea Holmes told the ABC.

"I spoke to her last Thursday and it was 'see you next week' and completely normal."

Police are still appealing for information about Preethi Reddy's final hours. ( Supplied: Facebook )

Many posted condolence messages on social media for Dr Reddy on Wednesday morning.

"I can't imagine the absolute pain Preethi's family and friends are feeling this morning at the devastating news that has come to light," one woman posted on Facebook.

"Sending my deepest sympathy and condolences to Preethi's family and friends … RIP you are now at peace."

"I'm very upset and shocked to hear this. I went to high school with Preethi," another woman posted.

Reghavee Goel has just moved to Kingsford and was shocked to hear Dr Reddy's body had been discovered nearby.

She said she noticed something was wrong about 9.30pm Tuesday when several police cars arrived near her home and "were here all night".

Police are still investigating the circumstances surrounding her death and are asking anyone with information to come forward.