Merseyside Police also released CCTV footage of the gunman running from the scene as they warned anyone helping him that officers would do “everything legitimately possible to bring you to justice”.
Detective Chief Superintendent Mark Kameen said: “It is beyond comprehension how anyone can protect a person who is responsible for killing a nine-year-old little girl.”
In an update on Thursday afternoon, Mr Kameen said work by forensic teams and the National Ballistic Intelligence Service (NABIS) revealed two firearms were discharged at the scene of the killing in Dovecot on August 22.
He said: “I believe at this time that the gunman brought both of these weapons with him and that they were still with him when he callously ran away from Olivia’s house.
“I want to know where those guns are now. ”
In a direct appeal to anyone who may have been told to hide or dispose of the guns, Mr Kameen said: “I understand you may be frightened of contacting us, but I want you to do the right thing for Olivia and tell us where they are right now.
“If you are hiding the guns and you have no intention of telling us, then I place you in the same category as the vile man responsible for the murder. And we will hunt you too.”
Footage showed the killer, dressed in a black padded jacket, balaclava with a peak, gloves, and trainers with white soles, running along Finch Lane, away from Kingsheath Avenue where Olivia was killed, and into Berryford Road.
Mr Kameen said: “We know this man is climbing through gardens and through people’s backyards in order to avoid being identified as well as using the roads.”
The man was described as 5ft 7ins and slim.
Mr Kameen said: “I know there will be people out there who know who that individual is, know that he is responsible for that murder and are now actively engaged in ensuring that we don’t locate him.”
He added: “This man is toxic. He is toxic to our communities and if you are protecting him he is toxic to you and your family.”
Mr Kameen said police were also releasing footage of a man who was in the area at the time of the shooting who they wanted to trace.
He said: “I’m interested in speaking to him as he may have information that is important to the inquiry by virtue of the fact he was in the area at the right time.”
Thanking the public for the “huge amount of information” they had given, Mr Kameen said: “The investigation itself has made significant progress, and the response from the public has been excellent and directly helped the enquiry. However, I now want to ask for more information and more help.
Olivia died after she was shot in her home when the gunman chased convicted burglar Joseph Nee into the property at about 10pm.
A post-mortem examination found her medical cause of death was a gunshot wound to the chest.
Her mother Cheryl was also injured and is still receiving treatment for her injuries, police said.
A 36-year-old man from Huyton and a 33-year-old from Dovecot were arrested on suspicion of murder and two counts of attempted murder in relation to Olivia’s death last week and have been released on bail.