The police were informed on Sunday about the incident. During inquiry, the alleged involvement of Murray Denis Ward, a British national and a frequent visitor to the institute, came to the light, the police said, adding that Ward had been associated with NAB as a regular donor for almost nine years.
Ward, who was subsequently arrested, allegedly inappropriately touched the three NAB inmates on September 2, the police said.
It was found that the accused had taken the inmates inside a room where he touched their private parts and tried to force himself on them, they added.
However, a caretaker at the institute, came there and Ward left the place. The three minors narrated their ordeal to the caretaker who informed the authorities about Ward's behaviour.
The institute then informed the police and the accused was arrested. He was produced before a court and is currently in police custody.
Police initially suspected it to be a case of sodomy. Police were probing whether he had sexually assaulted any other child at NAB since he was a regular visitor there. They were also questioning staff members whether they had seen Ward misbehaving with any other inmate.
His cell phone was being examined, the police said, adding that they had found a couple of "objectionable" video clips from his laptop. It is suspected that he had shared some clips through WhatsApp.
Ward, a native of Gloucestershire, the United Kingdom, had been working with Sterlite Technology Limited in Gurgaon till April.
He had suffered a paralytic attack in February and has been under treatment since then. He was staying alone here while his family is in the UK. Police suspect that he is a paedophile.