Imagine you're walking down Karangahape Rd on a wintry night in May, 1993. A small, red-haired girl in black boots and skirt is lounging on the footpath, waiting for a job.

Can you remember that moment almost 20 years later?

Probably not, memory expert Maryanne Garry says, but every rule has its exception, and the case of murdered teenager Jane Furlong could be one.

The 17-year-old mother who worked as a prostitute, went missing from her regular spot on K' Rd and wasn't found until earlier this year, buried in a sandy grave at Port Waikato.

Police, in launching a homicide investigation, have called for new witnesses to come forward, and are hoping for information that could lead to her killer.

Garry, a Victoria University psychology professor, specialises in human memory and distortion, and says people are extremely unlikely to suddenly "remember" Furlong.

"Memory fades very quickly. The biggest drop-off happens in the first 24 hours. It can be cut in half during that time," she says. "You add 20 years into the mix, especially if there's lots of media coverage, and things are only going to become more mixed up."

But there is a chance, Garry says, that people could realise the importance of something that had been lingering in their mind.

She's not talking about recovered memory – the evidence does not support that theory – but the idea new information can reconfigure memory and give it meaning. "For example, if you saw a black car and you thought it was strange, and remembered that, and then all of a sudden police said there was a black car connected to a crime, you might think, 'Oh, I hadn't thought about it in those terms before'."

The new information about Furlong's connection to Port Waikato might fall into that category, she said, and officer in charge of the case Detective Inspector Mark Benefield said that connection was critical.

Police had canvassed the area, and were also going back through information from the two previous inquiries to re-interview potential former witnesses.

He said sometimes all police needed people to remember were names, who they were hanging out with at the time, who else might have been around. "Time can be a small hurdle but there can also can be positives because allegiances change and people can be more willing to come forward."

However there were challenges, because a lot of the people involved in the prostitution scene didn't want to remember, or had moved on.

Some, including fellow K'Rd prostitutes Natacha Hogan and Leah Stephens, had also met with early deaths.

Stephens was killed three years before Furlong, by a client whom she witnessed committing a murder. Hogan, a friend of Furlong's, was bludgeoned to death in Symonds St cemetery in 1996. She and Furlong were due to testify in a rape case the day after Furlong disappeared.

Benefield would not say if the men implicated in those crimes were still on the suspect list.

"The important thing now is that people come forward. Jane was a mother, a sister, a daughter, an intelligent girl. And someone knows what happened to her."

KEY FACTS

Jane Furlong was living with her boyfriend when she vanished. Her baby was being brought up by his parents.

On May 28 Furlong went to be interviewed by police. She was to testify in a rape case, and was also a witness in a gang assault trial.

Later that night she was working on K Rd, dressed in a black miniskirt, black lace top, ankle boots and a brown leather jacket.

Some time around 10.30pm, she disappears and is reported missing by her boyfriend.

There is no sign of her until her remains are found by a dog-walker at Port Waikato in May this year.

Police believe Furlong may have been alive for some days after she went missing.

Detectives want to speak with a man recorded in Furlong's diary as "Tommy", with whom she may have planned to spend a night at about the time she went missing.

Anyone with information can contact the Op Darlia team on 0800675263, visit the What happened to Jane Facebook page, e-mail furlong@police.govt.nz or call Crimestoppers anonymously on 0800 555 111.

- © Fairfax NZ News