In the week a father killed his two daughters, a grieving grandmother asks: How CAN a man murder his own children?

As she pulled up outside her daughter's spacious Victorian home, Carol Quinn had a nagging feeling that something was very wrong.

She usually spoke to her daughter Claire every day on the telephone, but she hadn't heard from her for a week and was increasingly convinced something was amiss.

Whatever concerns she may have had, though, nothing could have prepared Carol for the sight that awaited her inside her daughter's home.

Claire and Phillip Austin

Before the troubles: Claire Austin with husband Phillip, who later murdered his wife and two children

Lying on the blood-soaked floor of the kitchen was 31-year-old Claire, who worked as an auxiliary nurse.

She had been stabbed to death with such savage force that the knife used to attack her had snapped. Next to her lay the family's poodle, Dandy, who had been beaten to death with a mallet.

Terrified, Carol raced up the stairs of the three-bedroom house, desperate to find out if her two grandchildren were safe.

In one bedroom she discovered eight-year-old Keiren, his lifeless body lying face down on the duvet, a teddy still on his pillow.

Then she stumbled into his seven-year-old sister's room to find her dead on her bedroom floor, the belt from her little pink dressing gown around her neck. Both Jade and Keiren had been strangled.

It was July 17, 2000, and by then her family had already been dead for several days.

If the horror of that scene was not shattering enough, what Carol and her 62-year-old husband Harry have never been able to come to terms with is that Claire and her children were murdered by Phillip Austin - Claire's husband.

Killer question

So how can a man be so consumed with wickedness that he is willing to kill his own children?

It is a harrowing question, made all the more pertinent by the tragedy which emerged this week after David Cass, from Southampton, murdered his two daughters and then committed suicide after separating from the girls' mother.

The double killing follows the story last month of Christopher Foster, who killed his wife and daughter, then set fire to their Shropshire mansion before taking his life because his business was failing.

Phillip Austin, then 31 and a warehouse driver, was later given three life sentences for the triple murders that destroyed Carol Quinn's family, but his motives remain as much of a mystery today as they were seven years ago.

Even now, the only reasons Claire's family have discovered are that he felt his wife 'nagged' him, and that the couple had financial problems.

Reflecting on the misery he has caused, 59-year-old Carol, who is retired from civilian duties with Northamptonshire Police, is remarkably dignified.

In the days before stumbling across that dreadful scene, she had become increasingly troubled because she had been unable to contact Claire.

Carol and her husband Harry - Claire's stepfather and a chief engineer for a flour mill - drove the 12 miles from their home in Bugbrooke, Northamptonshire, to check on her.

'It was the day that the missing schoolgirl Sarah Payne's body had been found,' recalls Carol, who also has a son, Matthew, 35.

Jade Austin

Strangled: Jade, seven, pictured weeks before her death

'I cried as I watched it on the news, unaware my own daughter was lying dead in her house.'

She adds: 'Shortly after the news bulletin I got a call from the secretary at my grandchildren's school asking if I knew why they hadn't been attending classes, and why Claire couldn't be contacted.

'Alarm bells immediately went off in my head. For a week, Harry and I had been unable to get hold of Claire either, despite leaving countless messages on her home and mobile phones.

'It wasn't normal - Claire and I spoke every day, often several times. I know it sounds odd but I decided that she and Phillip must have had a big fall out and that they were trying to sort things out.

'The last time I spoke to Claire was on Sunday, July 9. Harry and I had been to Hampton Court Palace the day before and she phoned to see if we'd enjoyed it.

'She and Phillip were taking the kids to see Chicken Run at the cinema that afternoon. When I called her that evening to ask if the film had been good, Phillip answered the phone. He sounded quiet and cold and told me: "We didn't go to the cinema. Something cropped up. Claire's not here."

'This was the day before he murdered them, and although the tone of Phillip's voice made me feel uncomfortable, Harry and I assumed they must have had a row.

'Phillip did have a temper and the one thing they always argued over was money. Phillip was dreadful with money whereas Claire, who was an auxiliary nurse, was a real saver.

'For the next few days I called morning and night and left messages on the answering machine, but Claire never called back.'

Claire, described by her mum as 'fun, fiercely loyal and loving', had met Phillip ten years earlier in Northampton. She had excitedly told her mum how she'd met a man who'd bought her a rose and asked for her phone number.

'Within weeks she brought Phillip home to meet us,' Carol says. 'He seemed quiet and unassuming. We could tell that he was a hard worker, but that he was never going to set the world on fire.

'If I'm honest, we'd always hoped Claire would meet someone with a profession and more ambition. But as long as she was happy - and she was - then we supported her.

Calm before the storm

'At that stage there wasn't anything to concern us about Phillip other than that he was useless with money. He would frequently overspend and then disappear in high dudgeon, which drove Claire mad. But there was no indication that Phillip might have a violent side.'

The couple worked hard, and within 18 months had bought a three-bedroom Victorian terrace in Northampton. The children soon followed, and on July 17, 1993 - seven years to the day before Carol found her daughter's body - the couple were married.

'The children were just gorgeous,' says Carol, her voice cracking.

'Keiren was our first grandchild and when Phillip called, elated, to say we had a grandson, Harry and I dashed to the hospital. I remember gazing at this little bundle and whispering to Claire: "My word, aren't you a clever girl, he's gorgeous."

'When Jade was born in April 1993, we filmed Keiren as he met his baby sister for the first time. Keiren was inquisitive and a real livewire, Jade was shy and sensitive.

'We loved taking them to the cinema to see films like Toy Story, and for days out at Legoland in Windsor. And we always took them to see a pantomime at Christmas.'

But if the two children revelled in their grandparents' affection, all was not well in their parents' marriage.

Carol recalls the moment nine years ago when she realised Phillip had a darker side to his nature.

'My grandchildren were sitting in our kitchen at our house when Keiren did something and Jade looked at him and said: "Don't do that or you'll get a good hiding, won't he Nanny?"

'I was a bit taken aback and explained that "good hidings" weren't something that we did in our house. "Well, Daddy gives them," Jade went on, before telling me something very alarming; that their father had started to put his hands around their throats if they'd been naughty.

'It concerned me greatly and I spoke to Claire about it the following day. She was shocked, said she hadn't known anything of this aggression from Phillip towards the children, but that she would see that it never happened again.

'Publicly, Phillip was the same as ever, and was always very involved with the children. They'd have days out at weekends like any family. I even heard Phillip talking to our local vicar at my aunt's 100th birthday party about the possibility of him and Claire renewing their vows.

Phillip Austin

Keiren, eight, before he was brutally murdered by his father

'In the first half of 2000, Claire and Phillip seemed happy and any money issues with Phillip appeared to be in the past. They went on holiday to the Canary Islands that June.

'Harry and I picked them up from the airport and they'd had such a fantastic time that within a fortnight Claire had booked a holiday for the following summer to Portugal.'

It was a trip they never took. The last time Carol saw her daughter alone was July 6, 2000. It was a Thursday and the pair enjoyed a shopping trip and lunch together.

'Claire was chattering away about holidays then,' Carol says. 'She told me they were hoping to splash out on a last-minute break in a few weeks' time. I suggested to her that it might be a good idea just to save their money, knowing what Phillip could be like if they overspent.

'"Mum, don't worry, we've got plenty of savings and we're getting on better than ever," she reassured me.

Yet unbeknown to me, Claire had confided in my niece that Phillip had been up to his old tricks again, wasting money and leaving them short.'

Four days later, Claire and her children were murdered. When DNA evidence and finger printing revealed that Austin was the killer, a massive manhunt was mounted. He was arrested five days later in Cumbria.

During police questioning, Phillip boasted about how he'd painstakingly planned the crime. He'd bought a mallet from a DIY store on the morning of the murders and used it to attack Claire in cold blood, fracturing her skull and her shoulder.

Forensic evidence showed there had been a desperate struggle, during which Claire had tried to escape through the front door, but Phillip had dragged her into the kitchen, where he stabbed her repeatedly with such ferocity that the knife broke.

Chillingly, he then drove calmly to Claire's work to inform her boss that she had damaged her back moving furniture and wouldn't be on duty later that day.

He then picked the children up from school and plied them with herbal sleeping tablets. He drove them around the country until late that night, by which time they were so drowsy that he was able to bring them home, take them upstairs to their bedroom and strangle them with little resistance.

Then he fled, taking with him a £5,000 loan he'd taken out for that specific purpose.

A week later, Carol Quinn uncovered the crime. 'I'll never forget the smell,' she says.

'And I'll never understand why I didn't sink to my knees and hug my daughter's body. But practical instincts took over and we raced upstairs to check on the children.

'We dialled 999 from a neighbour's house because we didn't want to touch anything in Claire's home for fear of destroying evidence. Instinct told me that Phillip was the murderer and I told the police so.

'That night Harry and I formally identified the bodies at Kettering General Hospital, then, two days later, we went to see them in the morgue. I stood holding my daughter's hand, and promised I would get justice for them, whatever it cost.

Mystery unsolved

'I still don't know why he did it. The police told me he's just an evil man.'

Even when Phillip confessed, however, there was little solace for Carol.

'Those first few weeks, if I managed to sleep at all, I'd wake up screaming and Harry would have to hold me to stop me kicking and punching,' she says.

'We had to wait a month to bury Claire and the children. I bought little outfits for the children to wear in their coffins and a top for Claire which she'd pointed out to me on that last shopping trip together.

'Then there was the heartbreaking business of clearing Claire's house, getting rid of the children's toys and clothes. I kept a cuddly hedgehog of Keiren's because he'd once asked me to look after it for him. It sits by a photo of him in my house. Every Christmas we hang a little cardboard angel that Jade made at school on the tree. I can't bear to light the candles that Claire bought me as a gift from her last holiday.'

Phillip initially pleaded not guilty to the murders on the grounds of diminished responsibility, but on March 22, 2001, at Northampton Crown Court, he dropped that defence and changed his plea to guilty.

'He showed no remorse as the judge gave him three life sentences,' says Carol.

'He even had the audacity to blame Claire for what he'd done. In police interviews he said she had driven him to it by nagging about going on another holiday when he knew they couldn't afford it. Claire didn't realise that Phillip had secretly taken out a £5,000 loan to fund his escape after the murders.'

Carol adds: 'Phillip has never contacted us since the sentencing. I don't know how he can close his eyes at night and sleep. I struggle to close mine because all I can see when I do is the bodies of my daughter and grandchildren.

'I always wonder whether Claire called for me when he was attacking her, whether the children called for their mummy as their father strangled them.'

The fallout from the murders has devastated Carol's family in different ways.

'My son Matthew was always very sporty,' she says, 'but now he spends £30 a month on medication for depression and high blood pressure as a result of this crime.

'In the months after the murders he was rushed to hospital several times with suspected heart attacks. They were actually severe panic attacks.'

Carol is undergoing counselling to cope with the horror of finding the bodies, and acknowledges her husband and son need it, too.

'Austin killed a part of all of us the day he murdered Claire and the children. My heart goes out to any other family which has suffered at the hands of a man so evil he can kill his children in cold blood.

'It's impossible to come to terms with the idea that someone has such a capacity for cruelty; it goes against the most fundamental human instinct to protect your children. Most people would give their lives to save their family.'

To add to her torment, Carol lives with the knowledge that one day Phillip will be set free from prison.

'He must never be released,' she swears. 'I worry all the time that one of these days he'll get parole. Thankfully, I had a letter only last week to confirm that, for now, he remains a category A prisoner - the highest risk to the public there is.

'Life should mean life, and he should die in prison. He took away his family's chance to live - why should he ever be given his liberty again?'