The relegation of a homicide as a cold case does not necessarily mean it is forgotten. And despite much publicised sentiment to the contrary, the same holds true for the Lynette Dawson case.

The term cold case is something of a misnomer, as at any time any small spark of new evidence can reignite the investigation and lead to the matter hopefully being solved.

Many investigators will approach cold cases from the perspective of an unsolved crime representing a miscarriage of justice, in that the rights of the victim have not been upheld and a guilty person is still free.

The term cold case usually refers to matters that are historical and remain unsolved, and the term is most often used in relation to homicide investigations.

Most states have specialist units attached to their homicide squads that deal specifically in cold case investigation.

In general terms a homicide investigation is termed a cold case when further investigations are deemed to be fruitless. This can occur when there is no identified suspect, there is insufficient evidence to prosecute a suspect or new information is required to progress any further investigation.

Cold case units will routinely conduct full reviews to see if there is any benefit to pursing a matter.

This was the case in the Dawson investigation, with NSW Police forming Strike Force Scriven in 2015 to review the circumstances of her disappearance.

A fresh set of eyes often needed

Police resources for this are finite so therefore a triage must take place.

Circumstantial homicide investigations present a number of challenges to investigators. ( AAP: Richard Wainwright )

In general terms police will look at putting resources into matters in the following priority: self-solvers, those that can be solved with minimal effort, are first, followed by those that can be solved with some effort. Last are those matters that are extremely difficult to solve.

An initial review of the available evidence and potential suspects is usually used to determine the above order and the likelihood of a successful investigation.

This process will usually involve and investigator who was not involved in the original investigations so a fresh set of eyes can look for new leads.

The media is a powerful investigative tool

Phillip Carlyle, pictured here with sons Ben and Stefan, was executed in 1997 on the Gold Coast. ( Supplied: Carlyle family )

In the Dawson case there can be little doubt that the extensive media coverage has pressured police into dedicating more resources to the investigation.

But more than that the media is a powerful investigative tool that can be used by police to apply pressure to suspects and gather new evidence. Exposure of cold cases in the media will often be co-ordinated with investigative strategies, including covert methodologies, in an effort to garner new evidence.

Cold case investigations usually take place over a period of years.

As a senior detective I had oversight for a number of years of the murder of Phillip Carlyle who was executed in 1997 on the Gold Coast. Local detectives continually put resources into this matter with this effort finally paying off almost 20 years later when three suspects were arrested in relation to his murder.

The Dawson matter differs from the Carlyle case in that there is no crime scene and the matter will largely be a circumstantial one.

Lack of a body no barrier to solving case

Circumstantial homicide investigations present a number of challenges to investigators. These can include a lack of crime scenes and forensic evidence, no body of the deceased to indicate cause of death and few witnesses to provide direct evidence.

In my career as a detective, I was involved in several circumstantial cases where the body was never found.

In 1999 I was part of the team that investigated the disappearance of a retired Yakuza boss on the Gold Coast. At trial it was alleged that his wife had strangled him and then cut his body up into pieces and left the body in plastic bags for garbage collection.

Despite an extensive search of the local garbage tip the remains were never located. The wife was convicted of murder.

In 1999 I was the arresting officer in the disappearance of young mother Michelle Baggott. She dropped her daughter off at school and was never seen again.

Her husband, Kevin Baggott, was convicted of her manslaughter after we proved a number of lies in the story that he provided to investigators. Searches failed to ever find her remains.

More recently, in 2010 I led the investigation into Stephen Pike, after the disappearance of his elderly mother. Despite intensive investigations her body was never located and her son was charged with her murder. He was convicted of her manslaughter and jailed for 10 years.

In circumstantial cases involving homicide it is crucial to be able to show a motive.

While a motive may not show an intent to murder, it does so a compelling reason for the murder. It also allows a jury to understand why the offender may have killed the victim and allows the prosecution to paint a picture that can bring together disparate pieces of circumstantial evidence.

In the case of the Yakuza boss and Pike, the motive was financial gain. In the case of Baggott it was anger at a wife who had left him.

Police don't give up on victims

Sorry, this video has expired NSW Police Commissioner Mick Fuller speaks to the media about an arrest in the Lynette Dawson case.

In all homicide cases the recovery of the remains of the victims is a high priority for investigators and the victims family so as to provide a sense of closure.

This was recently in the highlighted in the extensive search efforts for the body of suspected homicide victim, Matthew Leveson, in NSW.

Faye and Mark Leveson visited the Royal National Park in Sydney's south during a search for the body of their son, Matthew. ( AAP: Dean Lewins )

To address this a number of states have introduced no body no parole laws to force offenders to declare where their victims remains are and allow closure for their families.

When Kevin Baggott was released from jail 10 years later I went and visited him and asked where the remains of Michelle were, he refused to help and she still has not come home.

As the NSW Commissioner Mick Fuller said this week, "we will not give up on trying to identify the whereabouts of Lynette".

Charging Chris Dawson, the former husband of Lynette, is only the start of the process.

Dr Terry Goldsworthy is a former detective inspector with the 28 years' experience in the Queensland Police Service. He is now an Associate Professor of Criminology at Bond University.