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. ”
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.
“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.”
“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.
Olivia died after she was shot in the chest in her home when the gunman chased convicted burglar Joseph Nee into the property at about 10pm on August 22.
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.