All murder cold cases reopened in NSW

All cold case homicides in NSW will be reopened and investigated as police attempt to catch the killers.

NSW Police homicide commander Detective Superintendent Scott Cook said they want to give the families of victims answers, following the announcement the first 20 cases will be sent to investigators outside the homicide squad this week.

"The review process will look at the best opportunities to solve the matter, and cases that could be solved now given the right resources will be prioritised to be reinvestigated," Det Supt Cook told News Corp Australia on Monday.

All cases and previous lines of inquiry will be reviewed, with "priority" cases sent for further investigation.

"Every case is going to get reviewed and I am sorry to the families if their case is less solvable than others. It's not forgotten and it will be looked at again and again," Det Supt Cook said.

"I think most families will understand that we have to work on evidence and if the evidence isn't there - we could spend a lifetime searching for evidence that just isn't there."

The review team will look at potential witnesses, new technology and previous lines of inquiry.

Cases will be categorised into three sections, with the first matters set for review "unsolved" deaths that are clearly homicides.

The second is for matters that are "undetermined", including cases where it is not clear whether the person’s death was a homicide, misadventure or a suicide while the last category will include "unresolved" matters such as deaths where police may know who the offender is but they may be on the run or have been acquitted at trial.