Mr Coward said the ongoing investigation was very sad and difficult for all those affected by the death.
Police were continuing a "meticulous'' examination of the house where the shooting happened and a white four-door 1993 Ford Telstar which was driven from the property after the shooting and stopped in Waitara.
"We are very interested in hearing from people who saw that car on the roads between Okoki and Waitara, between 3.30pm and 5pm,'' Mr Coward said.
The victim's body will be removed from the house tonight and taken to Palmerston North for a post-mortem examination tomorrow.
The scene examination will continue tomorrow.
Child, Youth and Family this afternoon said it had been working with the boy, who was in the victim's care.
However, general manager Marama Edwards said the boy was not in CYF care at the time of the shooting.
"This is an immensely distressing time for the family and our thoughts are with them."
Ms Marama said CYF would continue to work with the police on an investigation into the shooting.
Detective Senior Sergeant Grant Coward of New Plymouth police said the victim's family was trying to come to terms with the sad situation.
"[Her] loved ones are naturally very distressed as are others who know the young boy."
The 13-year-old, who is not related to the victim, was stopped by police in a vehicle near Waitara a short time after the shooting.
Police are appealing for anyone who saw a four-door white 1993 Ford Telstar car, which was driven from the victim's home and stopped by police in Waitara and anyone who saw it travelling between Okoki and Waitara between 3.30pm and 5pm yesterday to call New Plymouth police station on 07 759 5500.
Detective Sergeant Coward said it was a very distressful situation that was affecting the community, some of whom went to the victim's assistance.