SEX abuse victim Derek Mulligan knew what happened to young boys who would dare to enter the old school in Derrybeg, Co Donegal, where he suffered so much at the hands of caretaker Michael Ferry.
So, after years of abuse, he returned to Ardscoil Mhuire every evening to stand guard -- and to warn other boys to stay away from the "devil" who abused him.
And when he finally built up the courage to confront Ferry at the school just 13 months ago, he was stunned by the response he received.
Despite claims from one of the college directors yesterday that Ferry only entered the premises under supervision, Derek remembers clearly what happened last June.
"I went to the school because I knew Ferry was there. I had just found out that he had abused other boys. I went to confront him," he told the Irish Independent.
"He was sitting in this big chair that he always sat in and there were no other adults there.
"I shouted at him, 'You've done this to other people'. He didn't care. He just looked at me and said, 'So you get it now, do you?'
"He was throwing it back in my face. I just exploded. He showed no remorse, no remorse whatsoever. It was just the cold way he said that to me, 'So you get it'. He is pure evil."
Between 2002 and 2010, Derek took it upon himself to protect other boys.
Pointing to a small wall where he sat every evening, Derek revealed: "I sat there. I sat there every night I could and if any boy came within a yard of the place, I chased them away.
"I did what I could. I knew Ferry was inside. He was sleeping in the place on a blow-up mattress."
The 24-year-old also revealed the victim of the first attacks -- for which Ferry received a suspended sentence in 2002 -- had travelled to Dublin on Monday to support him and the three other victims in the second case.
That man, who has since left Co Donegal, had agreed Ferry shouldn't be named in 2002 because the accused's mother was dying at the time.
"He had wanted to save the family from embarrassment and we understand that. He came to court to see Ferry sentenced," said Derek.
The full horror of the case is far from over for Derek and the other victims.
"I know I was the one who decided to speak out but I couldn't have done it without the other boys' support. They have been brilliant.
"You live with something like this all day, every day. And when you close your eyes at night, you have the nightmares.
"But I will continue to speak out because this man was allowed back into our lives and back into this community after he had already been placed on the sex offenders' register.
"I want answers and I won't go away until I get those answers. There has to be a full inquiry into what happened and people held to account."
He was supported in that call last night by retired garda detective Martin Ridge, whose book on sex abuse in the Gaoth Dobhair area, 'Breaking The Silence', exposed cover-ups by the Catholic Church.
Mr Ridge and other gardai were responsible for bringing paedophile priest Fr Eugene Greene and teacher Denis McGinley to justice.
Greene abused victims in 17 Raphoe parishes and was sentenced to 12 years in jail in 2000.
Mr Ridge said of the latest scandal: "It beggars belief that this has happened. This was going on in the same part of Co Donegal at a time when Greene was being sent to jail. McGinley was jailed in 2002, which also covers this time period.
"There are young people in the parish of Gaoth Dobhair and the surrounding areas who have suffered horribly at the hands of paedophiles and it is heartbreaking to hear it has happened yet again.
"This casts another dark shadow over the area and I believe that unfortunately there are others out there who have not, as yet, been brought to justice."
He added: "Derek Mulligan is a very brave young man. He is shining a light on another terrible episode. I want him and the other victims to know that there is light at the end of the tunnel. By speaking out, they are helping themselves and so many others."