It was one of the major holes in Keli Lane's defence — no witness had ever seen her at the Sydney unit block she claims to have visited multiple times for sex with "Andrew".

Police found no evidence to support Lane's story about an affair with the father of her missing baby, the man she claimed had Tegan.

Now the ABC's new documentary series Exposed has found a former resident who was never interviewed during the police investigation, and who has identified Lane as the "sandy-haired girl" he saw leaving the building on multiple occasions late at night.

Darryl Henson was living at Wisbeach Street in Balmain during the summer of 1995/96, when Lane claims to have had a sexual relationship with Tegan's father Andrew in another unit at the building.

Keli Lane pictured at her 21st birthday in April 1996. She is four months' pregnant with Tegan. (Source: Supplied) ( ABC: Supplied )

Mr Henson returned to New Zealand in October 1996 and was tracked down this year by the ABC's Exposed investigation.

He has identified Lane in a series of photos and said he saw a woman matching her description at the building.

"I saw Keli Lane leaving the apartment block," Mr Henson said.

"I'm confident 100 per cent that I saw her.

"I've got no reason to lie. I'd seen her coming and going through the carpark entrance, through High Street."

Keli Lane during the murder trial in 2010. ( Dean Lewins: AAP )

Lane was jailed in 2010 for murdering her newborn baby Tegan two days after giving birth at Auburn Hospital in September 1996.

She denies killing Tegan and told police she gave her to the baby's biological father, a man named Andrew Morris or Andrew Norris who lived in Wisbeach St.

But years later, during the murder investigation, police showed a photo of Lane to a number of Wisbeach St tenants from the time. None recognised her or said they had ever seen Lane at the building.

Do you know more about this story? Email exposed@abc.net.au

Exposed's investigation has revealed Mr Henson is among multiple Wisbeach St tenants who were never interviewed by police, despite attempts by detectives to contact him in New Zealand.

'I used to think she was brave'

A screenshot from the Exposed documentary outside the Wisbeach St apartment block where Keli Lane claims to have visited Andrew, the man she told police has Tegan. ( ABC )

Mr Henson said he saw Lane leaving the apartment block on several occasions late at night or during the early hours of the morning.

"It was quite late. It was dark. Sometimes 1:00am. Because I used to work on my car until the early hours of the morning," he said.

"I used to think she was brave because a lot of people were quite nervous of going out late at night, and she wasn't. She just went bowling out there. I thought she just knows her way around."

An image from the Exposed documentary showing how journalists worked out in which flat Andrew might have lived.

Despite claiming she visited the apartment numerous times, Lane told police she did not recall seeing any other tenants when she was coming or going late at night.

"She probably couldn't see me in the dark. But I remember her," Mr Henson said.

Because he was never interviewed by police, Mr Henson's evidence was not presented at the murder trial and the jury has never heard from him.

"If it's going to prove she wasn't lying about that, [the jury] should've heard from me," he said.

"It would be annoying to think that she wasn't believed, when she really did go there.

"The jury should've heard everything. They should've heard from me too, just to clarify I did see her."

Compelling new evidence

Dr Michele Ruyters says she believes the Keli Lane matter rates as one of the most high-profile injustices in modern Australian history ( ABC )

The director of the RMIT Innocence Initiative, Dr Michele Ruyters, has been studying the Keli Lane matter and believes the potential for a wrongful conviction is "high".

Because Lane has exhausted all avenues for appeal, Dr Ruyters says her conviction can only be reviewed if fresh and compelling evidence that wasn't heard in her trial is brought to light.

"If Keli Lane had been seen in the vicinity of Wisbeach St, in or without the company of Andrew Norris, that immediately suggest that her story has an element of truth," Dr Ruyters said.

"If this was a witness who was not previously identified and not called, that would be very compelling evidence.

"That would be very significant."

Dr Ruyters believes the Lane case rates as one of the most high-profile injustices in modern Australian history, based on the Innocence Initiative's own analysis.

"Where a person can be convicted based on a narrative that's constructed by the prosecution and supported by an incomplete police investigation," she said.

"I think it says something that the jury was prepared to accept that situation.

"I would have called it this century's Lindy Chamberlain. Except in Lindy Chamberlain at least there was some forensic evidence that was later disputed.

"I think it's enormously problematic that people find it easier to accept that a young mother would kill her child than a young man might accept responsibility for that same child."

A young Keli Lane at a water polo competition. ( Supplied )

A police investigation concluded that nobody by the name of Andrew Morris or Andrew Norris lived in the building at the time. Andrew Morris/Norris has never been found or come forward.

Baffled by a 'frustrating' case

Although Tegan Lane's body was never found, former NSW Coroner John Abernethy said he believes Keli Lane never "handed the child over to anyone".

"The only person who knows what happened to Tegan Lane ... is her mother," Mr Abernethy said.

"I think the evidence that she's dead is overwhelming. A Supreme Court jury formed the same view."

But Mr Abernethy has told the ABC he remains baffled by the failure of everyone involved in the case to find Tegan.

"Tegan Lane was arguably the most frustrating case I did. It was a case that I simply could not solve," he said.

Sorry, this video has expired Keli Lane calls Caro Meldrum-Hanna from Silverwater Correctional Facility

Lane gave several different versions of events about what happened to Tegan when she was first confronted by authorities in 1999, including denying she had ever given birth to Tegan.

She was sentenced to 18 years in jail for Tegan's murder and three counts of making a false statement on oath. She's eligible for parole in 2024.

Exposed will air at 8:30pm tonight on ABC TV and is available on iView.