He regularly entertained families and school groups at Hartlepool Historic Quay where he worked as a volunteer.

But as he gave displays of musket, cannon and pistol firing, visitors were unaware of the evil sex acts he was responsible for as he lived a bizarre double life.

His home was full of toys, dolls and uniforms and even had a male blow- up doll dressed in a schoolboy outfit.

Karnstein was well known to the local children because of his bizarre collection which included models of Daleks from TV's Doctor Who.

A spokesman for Hartlepool Borough Council said Karnstein was never employed at Hartlepool's Maritime Experience and undertook a volunteering role with an external group at the site.

A CRB safety check was carried out. But the court heard he had no previous convictions.

The spokesman added: "One of our staff noticed behaviour which they felt was inappropriate in May 2008 and he was immediately asked to leave the site and asked not to return.

"The matter was subsequently passed to the police. Our staff are trained to be vigilant at all times and at no point was there a danger to children visiting the attraction."

Stunned neighbours in Benmore Road where Karnstein lived reacted with shock to the news of his jailing.

One 67-year-old resident, who did not want to be named, said: "He was a bit of a loner, but he seemed like an ordinary kind of guy.

"We saw the police taking things from his house, but I never would have suspected anything like that.

"It is shocking and you don't expect to hear about this kind of thing in your street.

"This is what you read about happening in other places, not where you live."

Another resident said: "He seemed like a quiet man. He would stop and say hello but that was about it, he kept himself to himself."

Another Benmore Road resident said: "I didn't know him that well and I don't think many others did to be honest.

"He used to live with his mum and you would often see him walking his big Great Dane, until a few years ago.

"He didn't really say much."

Meanwhile, police have praised the courage of Karnstein's victim for coming forward and pledged to follow up any reports of abuse no matter how long ago.

DC Stuart Robinson, of Hartlepool CID, said: "Even though many years may have passed with such historic crimes, they are still taken very seriously and are fully investigated.

"Wherever possible we will bring offenders to court and seek justice for victims of crime."