A man has been arrested on suspicion of murder and attempted murder over the killing of nine-year-old Olivia Pratt-Korbel.
The 34-year-old from Liverpool is being questioned by detectives from Merseyside Police.
Two other men, aged 29 and 41, have been detained on suspicion of assisting an offender.
Olivia was shot when a gunman chased another man into her home in Dovecot, Liverpool, on 22 August.
The man arrested on suspicion of murder and attempted murder was detained in Runcorn in the early hours of Sunday and is being held in custody, police said.
The 41-year-old, from Knowsley, Merseyside, was also arrested in Runcorn.
Police said the 29-year-old man was arrested later after officers executed warrants at two addresses in the "Liverpool area".
Det Ch Supt Mark Kameen, who is leading the investigation, said: "We still need the public's help in ensuring that we can a build a strong evidential picture so justice is served for Olivia and her family.
"I appeal for those who may have information – no matter how small – that could continue to help our inquiries, to contact us directly or anonymously and we will do the rest."
Olivia was shot in the chest by a gunman who had chased convicted burglar Joseph Nee into her home.
Neither of the men who entered the home had any links to her family.
Her mother Cheryl was shot in the wrist as she tried to shut the door on the attacker but he fired two more shots at the man he had pursued, Merseyside Police said.
On Tuesday, the opening of the inquest into Olivia's death heard how an armed police officer had tried to save her life, pressing his hand on her wound as she was taken to hospital in the back of a police car.
Merseyside Police had previously arrested two men on suspicion of murder and two counts of attempted murder but released them on bail a week ago.
One of the men, aged 36, had been recalled to prison after breaching the terms of his licence.
On Saturday, a minute's applause was held in tribute to Olivia during the ninth minute of the Premier League match between Everton and Liverpool.
The Merseyside derby also featured a police appeal for information and an anti-knife and gun crime banner was unfurled, stretching across supporters from both clubs.
Olivia was one of four people fatally shot or stabbed within one week in the region.
Her funeral is due to take place at St Margaret Mary's Church in Dovecot on 15 September and her family has asked mourners to wear a "splash of pink" for the service.
A crowdfunding page set up to support Olivia's family has raised more than £40,000.
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