A £200,000 reward is being offered for information leading to the conviction of those responsible for murdering nine-year-old Olivia Pratt-Korbel.
It is the biggest reward in Crimestoppers' history.
The charity's founder and chairman, Lord Ashcroft, had previously put up £50,000 but the reward was increased after a private donor offered £100,000 and the businessman matched it.
"This case has been incredibly shocking, not just for those who are directly affected, but also for Liverpool and the nation as a whole," Lord Ashcroft said.
"I am delighted that with the support of a private donor, Crimestoppers can now offer a record £200,000 for information to catch Olivia's killer."
Olivia was killed in Dovecot, Liverpool on 22 August after a gunman fired shots into her home at about 10pm as he chased another man.
The schoolgirl was hit in the chest as she stood behind her mother, who was injured after being struck in the wrist by the same bullet.
Nine men have been arrested so far in the investigation, but they have all been released on bail and no one has been charged.
Police said on Wednesday that officers had spent 15,000 hours on the case, that there were 2,000 exhibits, and that thousands of hours of CCTV had been looked at.
Detective Chief Superintendent Mark Kameen said the man who was chased and shot by the killer remained in hospital.
He revealed the weapon used to kill Olivia was a .38 revolver; and that a second gun which was fired in the initial stages of the incident in Kingsheath Avenue was a Glock-type self-loading 9mm pistol.
Before the night of the killing, the Glock was used in two previous incidents on Merseyside in the last two and a half years.
The first was in Wimbourne Close, Dovecot, on 27 January 2020, when a 19-year-old man was shot. One of the bullets went through the front door of an innocent member of the public.
The second was on 8 August 2022, two weeks before Olivia died and a short distance from her home. Two rival groups, one in a car and the other on motorbikes, fired shots "indiscriminately" near playing fields in Finch Way, Dovecot.
Mr Kareem said: "This occurred in the middle of summer in an area where innocent local people would have been enjoying the park.
"Once again, as with the first time this weapon was used in our communities, we find that those in possession of it have no care, thought or loyalty for anyone else or their safety.
"Once again, they do not deserve anyone's loyalty."
A fortnight later, three shots were fired from the Glock in the shooting at Kingsheath Avenue, along with two shots from the revolver.
Mr Kameen said a renewed push to target organised crime over the last month had led to more than 600 arrests; more than 1,800 stop-searches; 142 warrants; 127 open land searches and 148 vehicles seized.
He said officers have worked more than 15,000 hours on the investigation, trawled through thousands of hours of CCTV and investigated more than 400 pieces of intelligence passed on by the public.
Crimestoppers is independent of the police and takes information about crime completely anonymously.
People can contact the charity via its website or on 0800 555 111.