Those whose loved ones were murdered by parolees are left devastated by crimes they believe should never have been committed.

Locked up then let out, career criminals are awarded 'get out of jail free cards' time and time again, only to continue to re-offend while on parole.

The aim of the Parole Board is to release offenders who are no longer considered a risk to society, yet almost half the time they get it wrong. According to the Bureau of Statistics, within two years of being released 41 per cent of prisoners are back behind bars.

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Shirley and Allan Irwin's two daughters were murdered by a career criminal while out on parole.

23-year-old Colleen and 21-year-old Laura were renting their first apartment together since leaving home. What the girls didn't know was the man living next door was about to savagely cut short their dreams, their hopes and their lives.

On a Friday night in 2006 in Melbourne's west, he cornered them in their home, brutally raping and stabbing them to death.

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Allan and Shirley cling to their memories but believe this unbearable heartache could have been avoided. Murderer William John Watkins's record dated backed to 1985 and included convictions for rape, aggravated burglary and assaulting police.

The maximum sentence is more than 40 years but he was given four years and released after just two and a half.

"Had she known he was on parole there's a fair chance she could have gone to the police station and said 'this bloke is harassing me'," Shirley said.

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Watkins was fatally shot by police three days after the murders, when he bashed an officer in WA after being pulled over for stealing petrol.

Allen and Shirley were thankful they didn't have to go through the justice system to see Watkins punished, but the same can't be said for Noel and Beverley McNamara.

Their 29-year-old daughter Tracey was raped and bashed.

"She went out that night and the next thing we get a call from the Ferntree Gully hospital saying she was unconscious," Noel said.

She died after two days on life support.

Rather than serving twenty years for rape and another 25 years for murder, her killer and rapist Noel Meyers, was sentenced to twelve years and freed after ten.

"I don't think I've ever felt so angry in my life," Noel said.

Helen Wicking's daughter Joanne was murdered, brutally tortured and stabbed by Sean Maraffko - a murder committed just three weeks after Maraffko was released from prison.

"A violent prior history and he was just allowed to get out early and free," Helen said.

However criminologist Professor Stephen Smallbone from Griffith University, defends the system.

"My observations of the various jurisdictions around Australian indicate that sentences are becoming longer - and have been for a long time - and parole is increasingly becoming more difficult to obtain," Professor Smallbone said.

Noel McNamara wants concurrent sentencing scrapped, a criminal's prior convictions released publicly, and a minimum sentence for serious offences.

"The murderer could have murdered before and they are not allowed to know about it - and that's wrong," Noel said.

A recent police survey in WA found that 98 per cent had little faith in the judiciary, citing the sentences handed down by magistrates and judges is not tough enough.

We have asked the Attorney-Generals for their response to this story and we plan to follow up.

This reporter is on Twitter at @LyndaKinkade