I meet Jason Braham in a West London pub on a sunny day in September. He and his wife Julienne have come up to London from their new home in Wales where they have opted to live a quiet life as artists. It is the day before the anniversary of Lucy’s death and he and Julienne are preparing to go to a festival where a band will be dedicating their set to Lucy.

Jason talks to me about his daughter. He describes her as a "very good, friendly person" but says, "I don’t think she was a fool in this case. She knew the sort of character that Jaggs was. His is a fairly obscene bunch, really. She wouldn’t have normally had anything to do with him. The guy rolled up with this wretched cat.

"Since her death we’ve found a load more out about her as a friend from her pals, because you don’t necessarily know your own children incredibly well. I mean, you know them, but I hadn’t realised just how much fun she was. We always thought she was possibly even slightly reclusive because she would like her own space, and often didn’t like going out to the pub every night or anything like that. But, when she did go out, she was the life and soul, apparently."

Contrary to some reports in the press, Jason’s daughter and Jaggs were not friends. She was three years older than him and they only knew each other vaguely through their parents.

Both Jason and Julienne Braham taught Jaggs, at preparatory school and at Harrow respectively. He tells me what he remembers of Jaggs at Harrow.

"He was very clever; he had a very high IQ. He didn’t work particularly hard… his results weren’t particularly good. He left his first boarding house and went to another one, and of course we now know why. The question that people ask is if enough was done to follow that up. I suspect it wasn’t. It was an attempt to force sex on a boy, a junior boy and, later on, we also heard in court that that’s the way he saw sex in general, even when it was consensual. He obviously fantasised about raping someone… He obviously had some sort of obsession with her [Lucy] because that came out in court, but we didn’t know that; nor did she."

Jason expresses his conviction that staff at Harrow could have done more to prevent the sequence of events that led to his daughter’s death. "You’ve got 800 boys you’re responsible for [at Harrow]. I reckon he was a danger to them, given his past record, on that score, and he was a danger to all the daughters and all the wives and the other staff. But simply no one was thinking about it. No one was recognising that he was a danger.

"This might sound hard, but I do believe that pressure on teachers, above all, to achieve the ‘perfect score’ with their examination candidates, a knock-on effect of the obsession with the ‘league table’ as a measure of a school’s worth has impacted on their family lives and on their ability to take a balanced view of their role in the community. In a less frenetic time I am sure the degeneration of William Jaggs and the behaviour of his circle would have been addressed long before the crisis was reached."

He describes William’s parents, Alan and Stella, as being "a little too innocent" in the way they handled their son’s behaviour. He says, "They were too amateur in the way they dealt with the problem. Alan took Will away to the country, to try to get him away from the influence of the gang he was with, to get him away from drugs and his drug dealer, thinking this would cure him, or at least would help."

Despite this criticism, Jason seems tolerant and forgiving of Jaggs’ parents.

"My wife has had Stella round for coffee," Jason tells me. "Not to talk about the crime, obviously, but to talk about how she was coping. I think for me it would be difficult, actually. Knowing exactly what their son did to my daughter I’d find it quite difficult to sit down… although I don’t actually bear him [Alan Jaggs] any malice."

I then ask him how he feels that Jaggs is only to be detained in a secure hospital, rather than a prison.

"There is an illiberal part of me that would have liked to see him spend time in a regular jail first, where he would see just how foul even hardened criminals consider crimes like his. It would also serve to remind people that Jaggs is a criminal and not just insane."

When we broach the subject of Jaggs’ drug habits, Jason tells me that he has been carefully following reports about the dangers of drugs. He is clearly concerned about the possible link between cannabis use and mental illness. "A lot of those reports were from the nineties but I don’t think skunk had appeared on the scene until a few years ago. So I would have thought the effects on teenagers now, who will be starting with skunk, will be much more devastating. I think actually this is just the tip of the iceberg."

He tells me he is considering giving a talk at the festival he will later be attending warning about "drugs and teenagers and the general complacency of my generation and it’s acceptance of… how it’s inevitable that teenagers take drugs. I think some people, because they did drugs themselves… it sort of holds them back from speaking out."

Speaking about his daughter’s death, Jason tells me, "Obviously, we will never properly come to terms with it; it would be very hard. But we decided to try to follow our creative work; I certainly would have found it difficult to go back to Harrow, if not impossible. And I think actually they would have found it awkward, too, because other people involved are still there and you can’t just carry on as if nothing’s happened. I have said we’re going to take in young graduates to work alongside us as artists. When they leave art school it’s quite difficult to carry on making art; you want to get a job. I’m hoping we can give people the chance to spend up to a year with us, working alongside me as a potter or Julie as a painter. Because that’s, in a way, what we were doing for Lucy."