TWO children who saw their father beat their mother and two brothers to death with a hammer were being comforted by their North-East grandparents last night.

Seven-year-old Jack Bluestone and his sister, Jessica, six, were the only survivors when their father, PC Karl Bluestone, went berserk.

Detectives were last night trying to discover what drove the respected officer to launch the frenzied assault with a claw hammer before taking his own life.

PC Bluestone, 36, attacked his wife Jill and the couple's four children at their semi-detached home in Kent. He then hanged himself from the garage door.

Mrs Bluestone was brought up in Middlesbrough, and her parents, Alan and Judith Skerry, still live in the nearby village of Great Ayton.

She married PC Bluestone at a service in Middlesbrough in June, 1994, before moving to Kent.

The "committed and enthusiastic" officer was described by neighbours as a devoted husband and loving father but also as an "introverted man" who bottled up his feelings.

Police, many of whom were colleagues, were called to the house in Gravesend on Tuesday evening after Jessica raised the alarm.

They found a hammer believed to have been used in the killings.

Mrs Bluestone, 31, an accountant with Essex County Council in Basildon, was discovered dead in the kitchen at the rear of the house.

The couple's three-year-old son, Henry, was found dead at the bottom of the stairs.

Chandler Bluestone, 18 months, was discovered in his cot with severe head injuries. He died later in hospital.

Jack, who was found outside the house with Jessica, was last night taken off the critical list at Kings College Hospital, London.

Jessica ran screaming from the family home saying: "Daddy's trying to hurt me" and rang neighbour Daphne Lane's doorbell to raise the alarm. Although she was injured, Jessica was last night discharged from hospital.

PC Bluestone's parents, former Gravesham councillors Greg and Christy, issued a statement through the police, which said: "We loved our son. He was a man devoted to his children, dedicated to his job and filled with love for his wife."

Mrs Bluestone's parents were too upset to speak about their loss.

The family, including Jill's brother Peter and sister Julie, later travelled to Kent to comfort the surviving children.

Stunned local residents started laying floral tributes and personal messages outside the house in Marling Way.

Several neighbours spoke of hearing rows in the past between Mr and Mrs Bluestone. One said Mr Bluestone suffered from depression and had recently taken time off work.

Others said they considered PC Bluestone to be a "smashing bloke".

Peter Snelling said: "I can't believe what he has done to his kids. It seems so out of character as he adored them and they loved him."

Kent Police spokesman Mark Pugash said: "We cannot say whether there was a history of mental illness or depression at this early stage. This will form a key part of the investigation."

PC Bluestone also had a 12-year-old daughter, Samantha, by his first wife.