A former security guard who sexually abused a vulnerable teenage boy was already a convicted sex offender, it has been revealed.

Tony Hallam, 53, had been convicted of sex assaults on young boys in 1969 and 1971 but went on to obtain a job as a security officer working at the Norwich headquarters of the EDP publisher Archant - John Haywood, Director of the Guild of Security UK Ltd said" this case just goes to highlight the importance of vetting and licencing in the security industry, whether it is ontract or in-house security. It is the only way forward for the industry to rid itself of employees like this".

It was at the Headquarters of EDP's publisher that Hallam carried out one of the indecent assaults on the boy, who cannot be named for legal reasons but has Asperger's Syndrome, after taking him to a security room in the building, Norwich Crown Court heard.

Hallam, of Julian Road, Caister, near Yarmouth was convicted of two counts of indecent assault on the boy and one of inciting him to commit an act of gross indecency. But he was cleared by the jury of a charge of indecent assault and another of gross indecency with the boy.

He denied all charges.

The case was adjourned to July 18 for reports and sentencing, but judge Daniel Worsley told him: “This was a shocking and wicked sexual abuse of a particularly vulnerable boy whom you befriended.”

He said Hallam was in a position of trust, adding: “Heaven knows what emotional damage it will cause.”

He said Hallam would be going to prison for a “substantial” period and said: “It will be years rather than months.”

He said he was also considering putting him on an extended licence on his release from any prison sentence.

“In my judgement it's extremely important that after your eventual release from prison you are watched very closely so you don't damage other children.”

The court heard that Hallam had been 17 when he was first convicted of a serious sexual assault and indecent assault on a boy under 16, and he had been 19 when he received borstal training order for indecent assault on another boy under 16.

During the trial the court heard how Hallam had indecently assaulted the boy after he stayed with him in Wymondham where Hallam was living at the time before they went to a car boot sale together.

He is said to have plied the boy with cannabis and drink before sexually assaulting the boy.

He also committed an indecent act on the teenager after taking the boy into a security room at the Archant offices.

Afterwards he told the boy “it should be their little secret.”

The allegation came to light after the boy confided to his parents what had happened months later and Hallam was arrested.