But Vanessa Forsyth, Troy's sister, said efforts to contact the long-term prisoner became futile after she told police of their letters.

The Canberra Times this week published new claims about the hit-run death of Troy Forsyth on March 1, 1987, on Kent Street in Deakin.

The 17-year-old was run down by a Holden panel van, which fled the scene and was never found.

Fresh information - including allegations of a cover-up - have helped shed new light on the case, and have prompted the victim's family to begin searching for legal representation to bring about a fresh coronial inquest into the death.

A prisoner from Goulburn claiming to have knowledge of the crime was expected to be called to the original inquest in 1988.

The exact nature of what he knew was unknown.

Troy's mother, Valerie Tomkins, who sat through the inquest, said the convict was either never called, or was called but refused to give evidence.

Police say their records show the prisoner did give evidence in 1988.

Ms Tomkins went to meet the man two weeks after the inquest, while he was still in rehabilitation in Canberra.

But she says he refused to see her again after she told authorities of their visits.

In December 2009, more than two decades later, Ms Forsyth wrote to the same prisoner, pleading for any information that could help achieve a breakthrough in the cold case.

The prisoner wrote back, asking her to meet him at Goulburn jail about her brother's death.

''Please I ask you to come alone, you tell no one, you talk to no law until we've spoken,'' the prisoner wrote. ''I'll know in your eyes. Honesty is all I ask.''

Ms Forsyth says she replied and organised a time to visit.

About two days later, she says she then told police she had a letter from him at her office in Mitchell.

''They were at my workplace within half an hour when I said I had a letter from him,'' she said.

''Literally within half an hour they were at my work and were taking photocopies of this letter.''

She says further attempts to contact the prisoner were fruitless.

He did not respond to her messages, and she has had no more contact with him since.

But police say they received the letter in September 2010, when Ms Forsyth met with the then lead investigator.

They say the letter provided no new evidence on the case.

Ms Forsyth still holds deep suspicions about the blue Holden panel van that was pulled over as it tried to drive back past the crime scene on the night of her brother's death.

That van was briefly inspected by police, but was allowed to drive away after the officer took the driver into his police car to talk for five minutes.

The officer, who was manning a road block, deemed it to be the wrong colour and believed the damage to its front end was old.

The driver sold the van in the following weeks and it was never re-examined, despite police realising nine months later there had been an error in forensic analysis of the paint fragments.

Ms Forsyth believes the driver responsible was let off for unknown reasons.

''I really believe that the person who did it had police connections, or had information about something bigger,'' she said.

''And why are people so scared to talk? It's obviously because something bigger, or bigger names or something have been thrown into the mix.''

She is pleading with anyone who has information to come forward.

''Who in their right mind would allow a 17-year-old kid to be killed and then just walk away from that?'' she said.

''How can they sleep with that?''