Apart from the fact of another human death, she knows it will take resources away from the case of her own daughter.

Megan Mulquiney disappeared 36 years ago, and, despite re-opening the case several times over the years, police are no closer to cracking the case.

Dorothy Mulquiney has learnt to live with sadness and unresolved grief - she has never moved from her south Canberra home, and never stopped wondering what could possibly have happened to her 17-year-old daughter.

But she says the ACT police, in deciding to reopen the case two years ago, have done more harm than good for her grieving family.

"When they say they're opening up your daughter's case, and you wait and wait and then find out they haven't got past square one - it's really nasty to hear as a mother," she told The Canberra Times.

Megan was a Year 12 student at Narrabundah College, and had a weekend job at Big W in Woden Plaza back in 1984.

She left work at midday on Saturday July 28 - 36 years to the day on Tuesday - left the mall on her way to the bus stop and never made it there.

Mrs Mulquiney said Megan had been such a reliable girl that she had started to worry within an hour of her not returning home.

There have been few leads in the years since, and just one suspect - convicted rapist Paul Vincent Phillips, who lived in the area at the time Megan disappeared.

He abducted another 17-year-old girl outside the Woden Plaza just two months after Megan's disappearance, and was caught within 24 hours.

He confessed to that crime, as well as to several others before and since, and spent most of his adult life in and out of jail.

Although he was never charged in relation to Megan, he was identified as a prime suspect during a 2009 inquest that found it extremely likely Megan was murdered.

Phillips gave evidence at the inquest in front of Mrs Mulquiney and her family, but while he spoke chillingly and candidly of his various other crimes involving young women, he maintained he had nothing to do with Megan's disappearance.

He died in April, 2018, and police reopened the case later that year, saying a number of people had been in touch with new information.

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Mrs Mulquiney described the news at the time as a "godsend" - a glimmer of hope that new evidence might finally come to light.

But since that announcement, Mrs Mulquiney said she had heard very little from the police.

Aside from a curious call-out relating to an almost unintelligible scribble in a discarded copy of Australian Women's Weekly under a story about Megan in January 2019, there have been no new developments in the case.

ACT police have also repeatedly refused to discuss Megan's case publicly, saying only that it would be "inappropriate" to comment on an ongoing case.

"If and when we can make comment on this investigation we will," they said in a statement this week.

Mrs Mulquiney said reopening the case had caused her and her family untold stress, especially as it had become clearer as the months went on that the ACT police were not resourced enough to work full-time on cold cases like Megan's.

"These cases should all be looked at, but they just don't have the people," she said.

Ultimately, she said, she thought the answer might be more simple than the police theories, and that she had never believed that Phillips had anything to do with Megan's disappearance.

She thinks that on a busy Saturday in a crowded car park, Megan would have climbed into the car of someone she knew, and that whatever happened afterwards could well have been an accident.

"Paul Vincent Phillips was a horrible man, but the main thing I wanted was for [the police] to be able to rule him out," she said.

"I think the answer is looking at them ... In my mind, as a mum, and Megan, the type of person and daughter she was, I can't think why somebody would want to murder her.

"Maybe, maybe something happened and it got out of hand, I don't know. But I can think that way, and also in my own heart I do believe it was somebody she knew, and they wouldn't deliberately go to murder her."

She said she did not bear the police any ill-will, nor did she want retribution for whoever had taken Megan - too many years had passed.

"I don't think like that. I don't hate, put it that way, I don't hate anybody," she said.

"All I want to know is what happened to my beautiful daughter, so that I can put her to rest."