In those days the giant computer needed to work in a climate-controlled environment – good for the machine but uncomfortably cold for workers. "It was freezing," she now says.

A friendly engineer taught her how to use an allen key to slip into the locked generator room, where she would crank up the temperature a few degrees. And then came the explosion – "I thought I had blown it up".

It was only when she finally opened the door and saw people running that she learned a bomb had exploded outside the police station. It was March 27, 1986, and a group of armed robbers had detonated a car bomb outside the Russell Street Police Headquarters, killing constable Angela Taylor and injuring 21 people.

This week the government introduced a law to stop Craig Minogue, the last man in custody for the crime, from applying for parole even though he has completed his minimum sentence.

Carole Spence and her small group of colleagues were working directly above the blast but may have been saved by the reinforced concrete needed to support the heavy computer system.

With D24 communications network damaged the payroll workers were immediately assigned to take emergency calls with no-one knowing if more bombs were planted.

For five decades Spence has worked for various government departments and private companies in office roles but she has been anything but a back room operator.

Now at an age when most people have slipped into retirement she has become a latter day Miss Marple at the Victorian Institute of Forensic Medicine working with police on cold case investigations.

In 1996 an administrative consultant thought it was a waste of space to keep thousands of medical files from pre-VIFM days when police doctors saw victims of sex assaults.

"Burn them, they are too old," the boss instructed. Spence point blank refused.

She knew first hand how important the material could be as she worked with the police surgeon Dr David Wells before moving with him to the VIFM when he was appointed clinical forensic chief.

"The cases were from the 1970s until 1996. Most of the victims will still be alive and I wanted to make sure we kept the files."

The hard copies, kept in no particular order, include doctors' notes, victims' statements, D24 notifications, clinical cards and random pieces of information. In isolation they were a waste of space but combined with DNA technology and fresh investigative techniques the files provide new hope in near forgotten cases.

But more of that later. First we need to find how a naive Catholic girl ended up working on serious criminal investigations. With her twin sister Dianne she left Brunswick's St Margaret Mary's after year 8 and began work at the army's Albert Park Barracks as a data processor in the 1960s aged just 14. In those days young typists banged data on to punch cards to feed a giant computer that had less tricks than today's smartphones (you couldn't hide it on your lap while checking your Facebook feed waiting for the traffic lights to change like every second knucklehead today).

The choice to enter the workforce at such an early age was based on necessity – as one of seven children they couldn't afford to stay at school. There were jobs around the country before she joined the police payroll office in 1983. Slowly police realised the computer could be used as an investigative tool and the data processors began by inputting the telephone book, then moved to working with taskforces hunting serial offenders. Then it was cutting edge. Now it is basic procedure.

When the payroll work was outsourced Spence was grabbed by the crime department and given one of its most secret roles with the Special Projects Unit (SPU) – the centre of Victoria's new phone tapping operation. Its first job was to eavesdrop on the suspects for the 1988 ambush murders of police constables Steven Tynan and Damian Eyre.

Spence says the secret equipment was set up on a secure floor at the St Kilda Road Crime Department Headquarters. "There were poles with wires running from them everywhere."

The main suspects included the notorious armed robber Victor Peirce, who would later be murdered as part of the Underbelly gangland war. SPU bugged Peirce, his wife Wendy, members of the notorious Flemington Crew armed robbery gang and recorded their conversations with journalists, mistresses, priests and lawyers.

For the former Catholic schoolgirl it was an eye opener, or more accurately an ear burner. "It is where I learned to swear. I couldn't believe the language."

Phone taps, particularly in those days were often muffled. The technology was basic, the suspects inarticulate and the language peppered with gangster slang, half-finished sentences and underworld secret codes.

She said police employed three typists from the Blind Institute believing their hearing might be more acute when every word could prove to be a clue. In one conversation armed robber Peter "Bubble Brain" McEvoy described details of a bank raid to his then girlfriend, "At the time, dead set, your life is on the … line, you know what I mean?. . . At the wrong time during that five minutes you run into a couple of … bank guards, you know what I mean? The wrong place at the wrong time and you're … dead."

Eventually Peirce, McEvoy and two others were charged and acquitted of the murders.

In 1991, Spence applied for a temporary position working with Wells with the police medical office. "David said he didn't like public servants and said I could start with three months. I said that was good as I'm not sure I will like you.

"For the first three weeks I had nightmares. You saw children who were victims and the mentally ill. It was so sad."

She learned to love the job and three months became six until the position became permanent. Working in the old Sexual Transferable Disease clinic in Little Lonsdale Street she would see traumatised patients and listen to the hypnotherapist search for repressed thoughts from witnesses and victims.

Not everyone was fans of their work and the office was once fire bombed but as Spence had a habit of shutting all the solid doors the fire didn't spread. Which was just as well because her room was filled with discarded and combustible Melbourne City Council Christmas decorations (she has always been a collector of sorts).

In 1995 when Wells moved to VIFM she followed. They stayed together until he retired in 2013 – a professional partnership of more than 20 years.

She saw first hand the compassion of the doctors who dealt with sexual assault victims. "There was one who relied so heavily on David." She would battle with her demons and occasionally relapse. Once Spence showered, clothed and provided her with perfume, providing her with some dignity before she was admitted to hospital.

"I think working here has given me a lot more sympathy for people."

Along with her full time job as records management and administration officer, Spence has a side interest in helping the sex crimes cold case unit find information on unsolved crimes.

A statement taken at the time might show the victim's current day recollections are consistent, a doctor's report might corroborate a police theory or a D24 record may help confirm a DNA finding.

So far police have requested information in 114 investigations and Spence has  retrieved information in 69 cases, ranging from the interesting to the vital. In one case the young victims described the ostentatious colour of the offender's car. Cold case police were able to match it with the vehicle owned by the suspect at the time.

According to Wells the files have turned out to be "gold" as they have proven to be the only link to the original crimes as many of the police records have been destroyed.

The files, he says, are particularly important as sex offenders may lie low for years between crimes. "There are repeat offenders who commit crimes year after year," he says.

"I would like to say it was due to Carole's masterful insight but let's be honest, she is a chronic hoarder. She has more shoes than Imelda Marcos."

Wells, now working in the Gaza Strip for the United Nations, says Spence has always been passionate about her job. "She is a real livewire, a Mother Confessor and intensely loyal."

He says when she was once pulled up by a mounted policeman for an alleged traffic infringement, "She said, 'If your horse shits on my car I'll sue you'. He let her go without a ticket."

Who knows how many of those cases would have remained unsolved if 20 years ago Spence had followed orders and destroyed the records. Slowly she is returning them to some order, a process that will take hundreds of hours, but will allow police easier access to a resource that will give victims of sex crimes some chance of justice.