Don Schell was taking a Prozac-type antidepressant when he killed his wife, daughter and granddaughter, then turned the gun on himself. His son-in-law sued the drugs company - and won £5m. Sarah Boseley meets him.

Tim Tobin was an ordinary guy with a wife and a baby daughter living in small town America and that was just fine. He and his family were simple, normal people, he says. They didn't want to be anything different. He and Deb, his wife and their nine-month-old baby, Alyssa, lived in Montana, but they spent a lot of time over the Wyoming border with Deb's parents, Don and Rita Schell, in the small oil town of Gillette. Alyssa was the first grandchild and everybody adored her.

It was the life they wanted. Tim and Deb expected to bring up their children in Montana, just as they had been brought up themselves - close to generations of people they held dear. But it all went shockingly wrong.

In February 1998, Deb and the baby were staying with her parents in Gillette. Deb was there for a break and stayed for two weeks because she got ill while she was there. Meanwhile, her father Don was feeling low. He had suffered occasional bouts of depression in the past and it had happened again. The doctor put him on an antidepressant called Paxil (Seroxat in the UK) - a drug in the same class as Prozac.

Two days later, Don Schell, the non-violent family man and doting grandfather, took a .22 calibre pistol and a 357 magnum in the middle of the night and shot dead the three people in the world dearest to him - his wife Rita, his daughter Deb and baby Alyssa. Then he killed himself. The following afternoon Tim Tobin found the scene of carnage that will stay with him as long as he lives.

For a while, he says, he was out of his head. Once he was able to think rationally again, he and Rita's sister and other family members tried to work out what had happened. Their conclusion was that Don must have been affected by the medication he was on. Nothing else made sense.

They sued GlaxoSmithKline, the British drug giant that makes Paxil, and won a historic victory in June. The jury awarded $6.4m (£4.7m), but it wasn't for the money that the family put itself through the trauma of the court case. It was to clear Don's name and to tell the world that there could be problems for some people with the class of antidepressants to which Paxil belongs, known as selective serotonin reuptake inhibitors (SSRIs).

In that, Tobin admits he is disappointed. "I really just did want to win, to say, OK, the drugs did do it - what's everyone going to do now? And of course, there's been nothing. I honestly believe until it's somebody of importance it will be very difficult to get any changes. Here I am, a simple man from Montana. I'm not exceptionally rich or famous or anything. Who's going to listen to me?"

Tobin is 33 now - a tall, gentle soul with an occasional quiet, self-deprecating laugh. After the death of his wife and daughter, he too wanted to die. He now has an inside track on the depression that sometimes overtook Don and feels more able to assess the chances of his father-in-law having been turned into a suicidal killer by it. He is certain it could not have happened without the drug.

"To go from a state where you are in serious depression and would hurt yourself to becoming a person who would do this to his wife and daughter and his granddaughter - a nine-month-old baby girl who can't take care of herself - he would have had to be so completely out of his mind and there was just no way."

Tim and Deb lived with the Schells for five months in Gillette, where Don and Rita had been since their marriage, before moving to Billings, a four-hour drive away. They still spent a lot of time together. "We were always very close and after Deb got pregnant even more so. This was the first grandchild on both sides. Everybody was involved and excited. My brother took a 48-hour bus ride so he could be there when the baby was born. That was how the whole family was."

Don was retired, but had a job for a few hours every day working as a pumper for the oil company, checking on the oil wells to make sure everything was running smoothly. He was a slightly reserved man, Tobin says, except with his family. "He was a bit of a father figure to me. I enjoyed spending time with him."

When Don was depressed, he says, he didn't act odd. Depression, says Tobin, "is a normal part of life anyway... If anything, he became more loving with his family when he was down because we'd all stick by him and he'd get very, very appreciative of that because we'd all say, 'It's OK.'

"Deb and I were both overly protective parents. I would never have left my nine-month-old daughter there - or Deb for that matter - in a situation I felt might get bad." Tobin had never seen Schell become violent. "He raised his voice. He liked things a certain way. But the most you can say is that he'd get irritable at times - and you can say that about anybody.

"He loved Alyssa. We used to laugh about it because he'd hold Alyssa and we'd say you know you've got to put her down at some point. He was just really the proud grandfather. He'd fuss over her and everything, and he'd ignore us."

When he starts to tell of what happened on that February night, Tobin's voice slips into a low monotone. There are things he doesn't want to recall. He spoke to his wife on the phone on Thursday evening. When he drove down to join them as planned the next afternoon, they were already dead.

"I last heard from Deb the night before it happened. We talked at least once a day. Deb asked me to bring some stuff down for her and I said, 'Do me a favour and call me in the morning to remind me.' I didn't hear from her, but didn't think anything of it and left early from work to get down there.

"I got there somewhere around 4pm and there was no one answering the door at the house. I thought they were out running errands. So I left and spent a couple of hours trying to find them. Finally I checked the garage and saw the cars were in there and noticed a light was on upstairs. "

A neighbour called the police. An officer arrived who said he was not permitted to force the door, so Tobin and the neighbour broke a window at the back. "I said, 'You'll just have to arrest me, then, because I'm going in.' And of course he understood - he wasn't going to arrest me. Then we ran upstairs. That's when I found everybody.

"I don't remember much until I got back to Billings a few days later. It's all a blur. I've had nightmares over what I saw. But I don't really remember, and I don't spend a lot of time trying to remember. I went to a therapist because I was in a pretty bad shape. I really felt like killing myself. My brother quit his job and moved in to babysit me because I was in such a mess. I was worthless. I was totally worthless."

Tobin went from wanting to kill himself to taking chances with his life - travelling across Australia, New Zealand and South America, mountain climbing, bungee jumping and hang-gliding. The worst that could happen had happened. Death held no fears for him any more. In the end, he found he just wanted to go home.

"My life has moved on. I don't live that thing every day. It's just that it's always there, as if there's a scab over it, and every now and then you reach a point where the scab breaks off and you have to deal with this painful, lonely time because there aren't that many people that understand it.

"I have to live that for the rest of my life. It's not every day, but my daughter's birthday comes around, our anniversary, or if I see a little girl who looks like my daughter I have a real hard time. I remember the way Deb smelled - the perfume she used to wear. I smell it every now and then and it really brings me back to ground zero for a while. I guess the thing is that I feel that way and then I bounce back a lot quicker than I did before."

Glaxo's representative in court, Ian Hudson, who now works for the Medicines Control Agency in the UK, argued that the occasional suicide or killing by somebody on Paxil is not sufficient evidence that there is a problem with the drug, considering the millions who take it. Tobin is outraged. Virtually all drugs can cause a bad reaction of some sort in a few people, he says. However small the effect is, there is no excuse for not investigating what is happening. "I don't think they've taken a proper look at the whole thing," he says. "We're talking about people's lives. Whether we are statistically significant or not, four people dead is too many as far as I'm concerned."