A MURDER investigation was under way last night after the death of a two-year-old boy suffering from severe head injuries.

Kyle Fisher - described by one neighbour as "always smiling and laughing" - lost his fight for life two days after being taken to hospital.

The death has shocked the close community on the Central Estate, Hartlepool, where Kyle lived.

The boy's mother, 19-year-old Clare Fisher, of Troutpool Close, and mother-of-two Susan Spencer, 34, of Millpool Close, have been arrested in connection with his death and released on police bail pending further investigations.

Last night, police said they were not looking outside Kyle's circle of carers for the killer. Detective Inspector Tony Hutchinson, of Cleveland Police's Murder Investigation Team, said: "We want to stress that there is no suggestion that anyone unknown to Kyle did this.

"We don't want people scared there's an indiscriminate child killer on the loose."

Det Insp Hutchinson said members of Kyle's family were distraught.

One mother-of-three regularly saw the boy playing in the street where he often stayed with a babysitter.

She said: "He was a normal happy little boy, always smiling and laughing. You would see him in the garden, he was playing all the time.

"He didn't seem troubled or anything and you would never have thought this could happen to him. Everyone on the estate is just shocked."

Police said that Kyle's babysitter called the ambulance service late last Wednesday saying he had collapsed at her home.

The only child was taken for emergency treatment to the University Hospital of Hartlepool.

A few hours later, early on Thursday, he was transferred under police escort to the paediatric intensive care unit of Newcastle General Hospital. He died on Friday afternoon.

Police have been investigating since Kyle was first taken to hospital but launched a murder inquiry yesterday after a post-mortem examination confirmed he had suffered severe head injuries.

Detective Inspector Michael Wall, a child protection specialist, is leading the investigation. He said: "We are determined to find out how Kyle suffered his head injuries.

"Medical experts are working with us to determine when his injuries were caused and how they were caused."

Forensic tests have been carried out at three homes on the Central Estate. The house where Kyle was found was still being examined by police yesterday and officers were making house-to-house inquiries.

Operations were being co-ordinated from a police caravan outside the house.

Tributes and messages of condolence have been left outside Kyle's home. Amid the teddy bears, toddler reading books and flowers, one message read: "To our friend Kyle, good night and God bless. We will always have you in our hearts."

Police are anxious to trace a taxi driver who picked up a 19-year-old woman between 11pm and midnight near the Bar Paris - 42nd area of Hartlepool last Wednesday and took her to the University Hospital.

Police are also appealing to anyone who knew Kyle and the people he was with in the days before his death to contact them on (01642) 302126.

l The death follows a separate incident last month in Hartlepool where a two-week-old baby boy was taken into intensive care.

The child, who doctors had feared could lose his life, was said to be "poorly" yesterday.

A man has been charged with causing actual bodily harm and a woman with neglecting a child in connection to the incident.