Police are carrying out an extensive search of land at a golf course for the gun that killed Olivia Pratt-Korbel.
Detectives investigating the killing of the nine-year-old, who was shot dead in her home in Dovecot, Liverpool, on 22 August, were using drones and divers to search West Derby golf club in Merseyside.
DCS Mark Kameen said the search was being carried out on information the police received after he had “promised that we would leave no stone unturned in our hunt for the offender and the guns used on that night”.
“Our search teams are being supported by the north-west underwater search team and the Merseyside police drone unit.”
He said the search would take place in the area where the old Deysbrook barracks used to be.
Kameen added: “My message to the offender is clear – we will not stop until we have the evidence to put you before the courts and behind bars. Olivia’s family are absolutely broken by her tragic loss, which has robbed a beautiful young child of the life and future she should have been looking forward to.
“Olivia wanted to be a teacher or a vet and her family have described her as someone who liked to laugh and make others laugh. She was an innocent young child in her own home, who should have been safe.”
He said the investigation team had been “working around the clock” but still needed to find the guns used in the killing.
“I would appeal to anyone who has information that could help us with our investigation to come forward. This offender and those protecting him are a blight on the community, and the impact they have on the decent people of the community is toxic.”
Olivia was fatally shot and her mother, Cheryl Korbel, was injured when a gunman chased a convicted burglar, Joseph Nee, into their home at about 10pm.
Nine men arrested in connection with her death had been bailed, police said.
Last week, the Guardian reported that gun crime had risen in two-thirds of police force areas in the past decade, despite a fall of 14% nationally.
