A man who sexually assaulted a six year-old girl in a toilet block following a tee-ball game has been jailed for more than four years, after a cold case DNA review of the evidence revealed his identity almost a decade after the attack.

Roland George Stayt, 49, was convicted of the vile assault on the girl in a public toilet in a Medina park, which had remained unsolved since 2006.

It was then that the girl was accosted, and then assaulted multiple times after she had gone into the toilet to fill a water bottle.

DNA testing on her underwear at the time failed to identify the attacker.

But in 2014, police revisited the case – and found matches to Stayt, who had been convicted of other child sex offences against two other young girls, and jailed in 2009.

Today, Stayt was imprisoned for four and a half years – as the young victim, who is now a young woman, looked on in court.

His lawyer had made an objection to the victim being present in court, which was denied by Judge Steven Scott.

The court was told how the girl was with her friends following a tee-ball game at Thomas Park in Medina when she was assaulted by Stayt.

He pulled down her underwear and sexually assaulted her twice, before asking her: “Do you like this?” She was unable to identify him at the time.

In 2009, the court heard, Stayt was convicted of various sexual offences against two girls aged six and three which included child pornography cases.

And in in 2014, police revisited the original case using up-to-date DNA technology – with results returning a probability of 1 in 590 million that the traces did not belong to Stayt.

He denied the offending at trial, but was convicted by a jury.

“This was a six year old girl who should have felt safe … and this offending is likely to have a long-term marked effect on her,” Judge Scott said.

He made Stayt eligible for parole, which means he could be released in two years and six months The mother of victims said that her "family is extremely grateful that justice has been served.

"When my daughter was assaulted all those years ago the police did everything they could to find the person but could not find him. So we tried to put it all behind us. Two years ago we were so shocked when the police call to say they had found the person," she said.

"Although the process was long and it took its toll on our whole family we couldn't have asked for better support from everyone involved including child witness services, the prosecutor and the police. We are thankful that the police re opened this case and the perpetrator is now in jail."

Acting Superintendent Peter Branchi from the State Crime Operations Division said the Stayt case one of the first identified for re-examination under the (then) new program of review of unsolved historical serious crimes initiated by WA Police in 2014.

"Seeking to take advantage of the significant advancements in forensic technology in the period since the physical exhibits were originally examined in 2006, investigators submitted the material for further forensic analysis in 2014. As a result a DNA profile was identified and matched to a profile on the WA DNA database," he said.

"WA Police is committed to investigating historical unsolved serious crimes, no matter how old they are, and will continue to utilise forensic technology as it evolves."