A paedophile at the Kincora boys' home in the North tried to get a child to have sex with an animal, a witness has told a public inquiry.
Senior care worker William McGrath was convicted of abuse at the notorious east Belfast institution and imprisoned in 1981.
He wanted to blackmail the victims if they later moved into political life, retired British Army officer Sergeant Q told the Historical Institutional Abuse (HIA) inquiry.
Sergeant Q said an alleged victim told him: "Look, to give you an idea of McGrath's perversions, he tried to get me to do it with animals."
Inquiry counsel Christine Smith QC said: "That was something that stuck with you over the years because ... while it might seem outrageous today, certainly seemed even more outrageous back then."
The inquiry is examining claims that intelligence agencies covered up the crimes committed by a paedophile ring in Kincora to blackmail some alleged high-profile abusers.
Police have dismissed claims a sex ring existed and said McGrath, Joseph Mains and Raymond Semple were working as individuals at Kincora before they were caught and convicted of abusing 11 boys.
It has long been alleged that other more prominent figures, including politicians, judges, civil servants and police officers, were also involved. It has also been claimed that McGrath, who had links to a shadowy Protestant paramilitary organisation known as Tara, was working as an MI5 agent.
Sergeant Q was instructed to interview an alleged victim of McGrath's at Thiepval Army Barracks near Belfast about political extremism.
He had been instructed that information about sexual perversions would be filtered out before being passed on.
The retired officer said: "It made my interview with him almost impossible to keep steering him away from that and trying to keep him to extremism topics."
Sergeant Q was a non-commissioned officer who served in the North between 1974 and 1976.
He was aware of "innuendo" around the homosexuality of Tara group members.
He said: "McGrath intended to use the abuse to blackmail the boys when they moved into political life."
The long-running HIA, chaired by retired High Court Judge Anthony Hart, is examining allegations of child abuse in children's homes and other residential institutions in the North from 1922 to 1995.