Detective Chief Inspector Dave Stevens added that the murderer could have been a paedophile who was targeting young girls.
Lin Russell, 45, and her daughter, Megan, aged six, were battered to death, together with the family terrier, Lucy, as they walked from school along an isolated country lane to their home in Chillenden, Kent, on 9 July. A second daughter, Josie, nine, survived a frenzied attack and although she was has been unable to speak properly since, she has been providing detectives with important clues.
Using specially constructed models and felt pictures, Josie has told police that she tried to flee from the attacker but he chased after her and dragged her back to the murder spot.
The police may consider holding an identity parade at a later date if they obtain strong evidence about one suspect, although a spokesman for Kent police, who are investigating the murders, said a "line-up" was unlikely at this stage.
More than 5,000 people have been interviewed about the killings. Extensive investigations into the background of Mrs Russell have revealed no evidence that she ever been stalked or received threatening telephone calls.
Det Chief Insp Stevens said: "I believe we have probably already spoken to the man responsible. There are over 5,000 people on our database but many of those people have been eliminated. There are a handful of people in the area on whom we are concentrating. It may be that the killer is a paedophile who was intent on harming the girls and Lin was in the way. It may be that he is psychotic or suffering from some mental problem. Whatever, he does not want to be caught. There was some degree of planning to this murder."
He added: "Josie has said that she was walking along the path with her mother and sister and they had to stand aside for a car to pass them. As she continued walking along the track she noticed the same car in front of her. The driver got out and removed a hammer from the rear of the car. The man attacked Josie's mother and Josie fled. She was chased and caught and returned to where her mother had been struck."
She has already been shown an E-fit picture of a man seen near the scene of the murder and had what police described as a "strong reaction. She was obviously very frightened."
Speech therapists have devised a special system of communication for Josie, who also uses a computerised voice synthesiser in interviews with police. She is being cared for at home by her father, Shaun, and attends Goodnestone primary school for simple lessons as she battles to recover from her injuries.
Mrs Russell and Megan were buried in Wales together with the family dog at a private funeral service last month.Reuse content