Robert Kingsley Whitehead, 84, will spend his final years being known as one of Victoria's longest-offending paedophiles after pleading guilty in the Melbourne Magistrates Court to 30 charges of indecent assault, two of sexual penetration of a child aged between 10 and 16 and one count of false imprisonment.

Whitehead's offending took place over 25 years. His charges involve six victims he sexually abused as boys or adolescents between the 1960s and the 1980s while working as a government railway officer or volunteer in historical train societies.

Fairfax Media can reveal that Whitehead was first convicted of a child sexual abuse offence and false imprisonment in 1959. Aged 28, he spent seven  months inside Pentridge prison before being released on parole.

Despite his 1959 sentencing judge Trevor Rapke requesting he never be allowed near young boys, Whitehead returned to his job as a Victorian government railway official employed in various roles which gave him regular contact with children.

Fairfax Media understands police records of Whitehead's 1959 conviction remained missing until last year. The missing records substantially weakened a previous police investigation into Whitehead in the mid-1980s, which resulted in no charges being laid.

Whitehead's case is likely to be referred to the Royal Commission into child sexual abuse, with victims and their families telling Fairfax Media that former senior Victorian transport officials and past managements of historical railway groups were warned of Whitehead's offending but failed to act.

Whitehead rose to become a controller at Spencer Street Station and held senior positions in historic rail societies at North Williamstown, Puffing Billy in the Dandenongs and in his later years, at the Seymour Heritage Rail Centre.

He was a member of the North Williamstown-based Australian Railways Historical Society from the early 1960s until he was expelled in 1976. The society's records give no reason for his expulsion, but Fairfax Media believes it relates to his predatory behaviour.

The society's president, John More, said he was ashamed of how previous managements had handled the issue of sexual abuse. Mr More was not involved with the society at the time of Whitehead's offending.

Whitehead was associated with Puffing Billy for about 20 years before being forced out due to a sexual assault allegation made in 1990.

However, some of the charges Whitehead pleaded guilty to on Friday relate to sexual assaults against an adolescent male at Puffing Billy in the mid-1980s.

Fairfax Media understands Whitehead was questioned by police in the mid-1980s about this and other sexual assault allegations. Despite compelling accounts from various children, Whitehead was not charged.

Another Puffing Billy volunteer, Anthony John Hutchins, was also questioned over abuse allegations at the same time as Whitehead. The pair even abused the same boy.

But where Whitehead denied any wrongdoing, Hutchins admitted to his crimes and was jailed after being convicted of 66 child sexual assault charges in 1986.

Puffing Billy chief executive John Robinson said management only became aware of concerns about Whitehead in 1990 when an allegation was made. Despite Whitehead's denial of wrongdoing, Mr Robinson said Whitehead's membership was cancelled and he was forced out.

The mother of one of Whitehead's victims has told Fairfax Media that she regularly rang Puffing Billy to warn about Whitehead's assault of her son well before 1990.

Mr Robinson said all Puffing Billy staff and volunteers had been subject to police checks since 2005 and working with children checks since 2007.

After being forced out of Puffing Billy, Whitehead became involved with the Seymour Heritage Rail Centre. It too faces claims it failed to act on warnings about Whitehead's abuse of children.

A spokesman for the centre said Whitehead had not been involved there for a long time and no one in a position of authority now had any knowledge of the matter.

One of Whitehead's victims on Friday said he was sickened to learn of his 1959 child sex abuse conviction. "He should have never been let near children again. But he was able to operate with a free reign for 40 years," he said.

Whitehead was released to his nursing home on conditional bail and is to appear before the County Court for sentencing on July 15.