A MAN found guilty of one of Wagga's most infamous murders - the sex killing of 18-year-old Sally Jones in 1987 - has pleaded guilty to the knifepoint rape of another teenager five months earlier.

Kenneth Barry Cannon pleaded guilty to sexual assault in Wagga Local Court on Wednesday.

He was committed for sentence in Wagga District Court at its next sittings starting September 15.

A "cold case" review of the rape of a 15-year-old in Bolton Park off Edward Street on November 8, 1986, led to the arrest of 54-year-old Cannon in February.

A 21-year jail maximum sentence handed down in August, 1991, for the murder of Miss Jones expired in 2012 and he is currently serving a sentence for the rape of a third victim - a 16-year-old girl on May 12, 1990.

Cannon used a knife as he preyed on young women in Wagga's central business district in the early hours of the morning.

Sally Jones was last seen alive leaving a Baylis Street night spot called Choices in the early hours of Easter Sunday, April 19, 1987.

Her body was found in the Murrumbidgee River at the Wiradjuri Reserve later that morning after Cannon told police he had discovered a pair of black boots and then drag marks along the beach leading to the river, as well as blood stains on the boots and sand.

Cannon, a 27-year-old mechanic at the time, told police he made the grim discovery while out jogging, but his trial was told he had never been jogging in his life.

Sally's body was discovered with 20 stab wounds.

A DNA profile of blood supplied by Cannon exactly matched a DNA profile of semen found on underpants on Sally's body.

A DNA profile taken from the underpants of the 15-year-old victim in 1986 also matches a profile taken from Cannon, according to agreed facts tendered to Wagga Local Court on Wednesday.

The clothing was kept by police for 27 years waiting for a breakthrough in the unsolved case.

According to the facts, the 15-year-old was walking along Edward Street past Bolton Park about 3.50am on November 8, 1986, when Cannon approached her.

After placing his arm around the girl, he said: "Don't make a sound unless you want to get cut".

According to the facts, the girl then realised Cannon was holding a knife with a 15cm serrated edge against her throat.

Cannon forced the girl into Bolton Park where he raped her and then let her go, saying: "I don't care if you report this or not, it's just one of these things".

The girl reported the incident to police and her clothing was kept for forensic examination.

The facts said a police cold case project team with the Department of Health's Division of Analytical Laboratories completed a review of the police investigation into the attack some months ago, leading to the DNA match and Cannon's arrest in February.

In September, 1991, the month after he was jailed for Sally Jones's murder, Cannon pleaded guilty to the May 12, 1990, rape of the 16-year-old girl.

She was snatched off Morrow Street near the Victory Memorial Gardens about 12.30am and raped at knifepoint in the vicinity of the Civic Theatre and the levee bank near the Riverina Playhouse.

Cannon was sentenced to prison until August 29, 2020, for that crime.

The rape and murder of Sally Jones was one of the darkest chapters in Wagga's recent history and created an atmosphere of fear in the community.

In sentencing Cannon, Justice Studdert described the murder as savage, most dreadful and most vicious.