Tuesday July 9 1996 is marked simply with a large black spot in my diary. How else would you denote the worst day of your life? My daughters Josie and Megan had been trying out Brownies after school, and Lin had accepted an offer from her friend Liz Gregson to take them there with her daughter at about 5 o'clock that evening. So Lin told me not to worry if they were home late, and I told her I would probably also be working late but that I would cook supper if I got home first. Lin kissed me quickly goodbye as we hurried off to school, and the last time I saw her alive was as she turned to walk back to the house through her lovely garden, with the dogs trotting happily at her side. At Goodnestone I dropped the girls off outside the school, where I last remember them clad in their pale blue gingham summer dresses running off to join their classmates.

At about seven that evening, I decided to return home, arriving at about 7.30 to an empty house with only our old retriever, Jackie, to greet me. I was slightly surprised, as I thought that if the family had gone to Brownies at 5pm then they should have been back by now. I assumed that they had stayed on for extra activities, or gone home with Liz Gregson and her daughter for a while. I vaguely thought that Lin might have rung me to confirm this, but there was no message on the answering machine. So I quickly set about making the dinner. At around 8.30pm the phone rang and I rushed to it, expecting Lin to be on the other end. But it was Liz, who told me that she had called at 5pm to take Lin and the girls to Brownies, but that the house was shut up with nobody home.

A feeling of unease spread over me as my mind raced for explanations. I told Liz the only reason I could think of for Lin's absence would be that Lucy, our dog, had escaped off the lead and got lost. I knew that Lin would scour the countryside in such a situation. Or perhaps Lucy had been involved in an accident and Lin had prevailed on someone to take them to the vets. But I could tell that Liz was worried. I said I'd telephone the local vets and she said she'd call back a bit later to see what I had found out.

I started phoning, only to find answering machines with messages to the effect that they were not open at this time. On an impulse I jumped into the car and drove along the road to Sandwich, turning up Cherry Garden Lane as twilight crept across the land. Why I thought they might still be somewhere along the route home from school I do not know, but I had to satisfy myself that they were not coming home late along there. I was still clinging on to the escaped Lucy notion. As I entered the tunnel of vegetation that enclosed the entrance to the lane, it was darkening and I switched the car's lights on briefly to see ahead. I drove swiftly up the bumpy track and emerged at the far end without seeing a soul. I had driven, without knowing it, just a few feet from where my family were lying in the bushes beside the track. I drove on all the way to the school at Goodnestone and then back again, but there was no sign of Lin and the girls.

It was now 9pm and I started an increasingly urgent round of calls, first to the local police station, which put me through to an operations centre that told me there had been no accidents reported that evening in our part of Kent. Over the next hour I rang hospitals further and further afield, but none had admitted anybody by the name of Russell, or fitting the descriptions of my family.

Just after 10pm, Liz rang back to hear my quavering voice on the other end of the phone telling her that Lin and the girls were missing. She shouted to her husband John to get the car out, they were coming over straight away, and as soon as she hung up I was on the phone again to the local police station. They now seemed genuinely concerned. The officer took down my descriptions of Lin and the girls, and where their last movements might have been. I was asked the inevitable questions about whether we had had an argument, or might Lin have had any other reason to take the kids away without my knowledge or consent. By now I was too worried to be overly concerned at the suggestion. The officer said that he would dispatch two constables to the house at once to get more details from me.

Liz and John arrived, followed by the police at about 11pm. I started giving them more thorough descriptions and telling them what I had already done that evening to find Lin and the girls. It was late enough now that I felt no embarrassment at calling out the police, but I was still clinging to the notion that a benign explanation could be found for Lin's and the girls' disappearance. The worst thing that I now considered was that one of them might have been involved in an accident. I tried to avert painful thoughts of one or other of the girls being hit by a car as they walked down the narrow lanes near to home. It never entered my mind that something more sinister might have befallen them.

The questioning continued and frustration started to impinge on the feeling of fear for my family's safety that was now consuming me. How long would this go on before the police started to do something? The question was answered almost immediately as, at about 11.30pm, a bus full of police officers skidded into the gravel driveway next to Granary Cottage, accompanied by a white van with a dog search team. At about midnight they set off in the direction of Cherry Garden Lane.

Now I was starting to go numb with worry. My brain was not allowing me to think beyond hospitalisation for one of the girls as the worst possible scenario. I was hanging on in a kind of limbo, with the vague hope that someone would arrive with Lin and the girls smiling and embarrassed in the back of their car, and some sort of rational explanation for it all.

I accepted another cup of tea from Liz and John and we spoke very little as we paced up and down outside in the driveway in the darkness. Lights glowed in police cars parked at the end of the drive, and radios crackled. Suddenly, at about 1am, another police car pulled into the parking area near to the houses. From the darkness emerged the two officers who had questioned me earlier. One spoke quietly to Liz and John while the other asked me in a subdued voice to accompany him back into the house.

Somehow I knew at that moment that the worst had happened. As we walked towards the house I trembled with dread. I had seen it in the movies a hundred times, and now this poor policeman was making the same moves, the same body language. We sat down at the kitchen table, with me still clutching my empty mug of tea, hardly able to breathe. He spoke quietly and with a quaver in his voice.

"I'm sorry to have to tell you, Dr Russell, that we have found your family, not far from here, and they have been in some sort of accident. It's very difficult for me to tell you this, but I'm afraid none of them has survived."

If I was numb before, now I entered a state of complete suspended animation. My external functioning switched on to autopilot and I drifted away into a kind of grey oblivion. Mentally, I had nowhere to go, nowhere to escape. The enormity of what was being told to me removed with one crushing blow any chance of optimism or happiness in my life. I have a vague recollection of seeing myself, as though from the outside, performing as if I were in a movie. I could hear myself slowly asking the policeman: Where? When? How? Surely not all of them?

He could only answer falteringly himself. He explained that the circumstances were suspicious, there seemed to have been some sort of attack. He said that in all his career he had never had to do anything so terrible as this. Liz and John shuffled into the kitchen, eyes red with tears; they had been told by the other policeman what had happened. They hugged me but I was cold and distant.

"Would you like some more tea?"

"No thanks."

"We will have to ask you to come to the police station in Deal to answer some more questions."

"OK."

"We will have to seal off the house tonight, would you like to sleep over with friends or relatives?"

"No thanks, I'll come with you now."

In my dazed state I started showing the police and my friends how to feed the cats and the dogs, and I asked them to be sure that there would be someone around to care for them and the ponies. John and Liz assured me that they would look after the animals.

I could not bring myself to ask any more detail of the police. Instead I turned in on myself, so that by the time a police car was detailed to carry me in the early hours of the morning to Deal police station I huddled up in the back like a lost and beaten child. Once out of sight of friends and neighbours, and in the darkness of the car with only an unknown police officer sitting beside me, I finally broke down. I remember shrieking with pain, and the tears rolling down my face. I shouted and swore, which I never normally do. "What has happened to them? Where are they? Why has this happened?"

In the heat of my rage my train of thought suddenly became more rational. "They were everything to me. Now they have gone, I have nothing left. Therefore there is no reason to go on living." And I started whining, "There must be an easy way out. Someone help me. Isn't there some sort of injection? It can't be too hard to find." The police officers tried to comfort me as best they could. But I could tell they longed for the cross-country journey down the winding east Kent lanes to be over. And in my delirium I too yearned for my life's journey to be over.

Later that morning, at about 6am, Ed Tingley - one of the family liaison officers who had been called to look after me - came into my room in Deal police station with a serious expression on his face. What he had to tell me changed everything.

He said that, although they had initially thought all of my family were dead, one of the children had survived. She had been rushed to a London hospital during the night, and was now on life support in an intensive care unit. My brain was galvanised with hope. There was a reason to go on after all.

The police and the hospital wanted to know which one of my daughters had survived. Ed asked me to describe them, and I told him that Josie had longer hair, whereas Megan's was cut shorter. He phoned the hospital and was told that the child in their care had short hair and so it was most likely to be Megan.

We arrived at King's College Hospital, south-east London. We were passed from reception to the head injuries unit and led to the front door of the intensive care unit. A nurse ushered us in and pointed across to the nearest bed. Lying on it, half submerged beneath a mass of pipes, wires and tapes, was a small, heavily bandaged figure. Her face was black and blue and puffed up like a balloon. Her eyes were tight shut, but by the freckles across the top of her nose above the oxygen mask, I knew her instantly to be Josie. I shouted out: "It's Josie!" before I was halfway across the room. Here was my reason for living, and if all she did was breathe, that would be enough for me.

Josie Russell had major skull fracturing, and serious brain damage impaired her speech. A week after the attack she was told that her mother and sister were dead. Later, Shaun Russell took her home to Granary Cottage for the first time.

On Saturday August 3, Josie finally got what she wanted and was able to lead me to our car, open the door and get in. Josie's favourite nurse, Marlene, had given up her day off to accompany us.

We pulled into the back yard and Josie immediately got out of the car and walked like a zombie towards the house. She tugged at the door until I caught up with her to open it. Once in the house Josie stood staring at everything that must have reminded her of her mother and sister and the life she had lost. She started upstairs with a wail growing in her throat, and burst into her bedroom. Her howling grew stronger and more anguished and she rushed through to Megan's room, grabbing one of her sister's teddies still on the dressing table. Then she plunged on into Lin's and my room, where Lin's clothes were still visible hanging on a rail. Josie was sobbing violently now and moaning like a wounded animal between her coughs and splutterings.

Josie continued her lament around the house for what seemed like an age, as we longed for her to cry herself out. Outside, the Kelly family had arrived with Josie's school friend Jazzmin. I pleaded with Josie to calm down and that Jazzmin was here to see her now. Slowly Josie started to settle and after a while was ready to go outside to see her old friend. Josie walked slowly out, and Jazzmin gingerly approached her. They came close, and Jazzmin handed Josie a little present. A smile flickered across Josie's face as she recognised Jazzmin, and I suggested to them that they go along the lane to see the ponies. Pauline, Marlene and I accompanied the two girls as they walked slowly ahead of us, Jazzmin talking softly to Josie. All Josie could say by way of reply was "uh" or "mm", or similar noises. But Jazzmin was not fazed at all; she acted as if she didn't even notice Josie's loss of intelligible speech.

We rounded the corner of the copse of trees that separated our house from the ponies' field. There in the distance were Tegid and Rosie. Josie looked across at them, with a quizzical expression on her face, as though she was not sure if these really were her ponies. But as they shambled across towards us, she ducked under the electric fence and moved quickly to meet them. She was smiling now and she reached out to greet her ponies with arms at full stretch. As Tegid came up she wrapped her arms around his neck and the tears flowed down her face. It was such a relief to see Josie crying with something akin to happiness.

Almost a year later, after a series of interviews with Josie, family liaison officers were able to piece together a detailed picture of the events of July 9 1996.

All I knew then and now is the following. At 4pm, Josie and Megan returned on the school bus from their swimming gala in Canterbury. Lin and Lucy were waiting for them, and they started on their normal walk home across the rape field behind Goodnestone, through the Woodpecker Wood and over the gate on to the by-road that leads past the entrance to Cherry Garden Lane. They walked down the lane to where it curves to the right and heard a car behind them. They stood aside from the car, and Josie waved to the driver as he passed. His face was grim and he did not acknowledge their greeting.

After he had passed they walked on around the corner to find his car parked broadside across the track. It was a few yards before the entrance to the Mount Ephraim house where Lin and the girls would have turned off the lane along the footpath to the Bruderhof community's grounds. If the bus had been back from swimming three minutes earlier, they would have been off the lane and along the path before the murderer drove by. If, if, if ...

The man got out of the car and reached in through the back window for a hammer on the rear shelf. He faced Lin and the girls and, according to Josie, he demanded money. Lin would not have been carrying any money with her on the school walk and she told him she had none. The murderer menaced them, and Lin asked him if he would come home with them and she would find him some money there. The man said: "No." I don't know if Lin urged Josie to run for her life at this point, or whether the man started beating Lin first. There is evidence to the effect that the man grabbed Megan and double looped a bootlace or drug tourniquet around her neck to hold her. Lin may have been rendered powerless by this hostage-taking. Josie has said that she ran away "when Lin was nearly dead", but this may mean that it all happened at once: Lin attempting to free Megan but receiving the first hammer blows; Josie seeing her mother injured and hearing Lin shouting for her to run away; Josie breaking away and running to the gate at Mount Ephraim; and the man running after her and dragging her back.

Forensic evidence and Josie's testimony point to the murderer then shepherding them all into the bushes and seating them on the ground. He methodically tore the damp towels from the girls' swimming bags into strips, and with these and their own shoelaces, he bound and gagged them. He tied Josie to a tree and asked her if the bindings were not too uncomfortable. He then walked around behind each victim in turn and rained down blows on their heads with his hammer until he felt that he had done enough. Josie remembers hearing Lin's dying cries. He meted out the same treatment to our dog, Lucy, although Josie does not remember at what stage of the murder our pet was killed. The whole encounter took about 15 minutes.

To write those few paragraphs in the summer of 2000, four years after the event, has required an immense effort of willpower. I have had to stare at my computer screen through a continuous stream of tears with my stomach churning and my heart pounding.

My mind wants constantly to leap on beyond the bald facts of movements and action, to how they must all have been feeling. The uncomprehending terror of my innocent and loving children at seeing and hearing their mother being beaten mercilessly and crying out in pain. Lin's horror and desperation in her last moments as, bound and gagged, injured and dying, her last hopes would have been for the survival of her children against the slaughter that was raining down on them.

That is why I don't want to know any more. Isn't it enough? I know better than any other how my wife and children acted and felt. Putting myself in their minds at the time of their death is like inviting death or madness upon myself. I could not save them; I must at least try to save myself.

In October 1998, Michael Stone, who has a personality disorder, was sentenced to life imprisonment for the murder of Lin and Megan Russell and the attempted murder of Josie. He is to appeal against the decision. Josie Russell is now in her second year at high school.

© Shaun Russell. Josie's Journey (BBC Worldwide, £16.99) by Shaun Russell is available now. Josie's Journey will be shown on BBC1 on November 1 at 10.35pm.