Police have arrested a 34-year-old man on suspicion of the murder of Olivia Pratt-Korbel.
Nine-year-old Olivia was shot in the chest at her home in Dovecot, Liverpool, on August 22.
Her mother, Cheryl Korbel, 46, was injured as the gunman chased convicted burglar Joseph Nee into their property at about 10pm.
Merseyside Police said on Thursday evening that a man from the area has been taken to a police station where he will be questioned by detectives.
Officers said the investigation into Olivia’s murder is ongoing and continues the appeal for information.
The reward offered in the hunt for the killer had been increased to £200,000.
The youngster was rushed to Alder Hey hospital in a critical condition but was later pronounced dead.
Her death followed months of growing tensions in the area and is thought to have been the latest incident in a series of tit-for-tat gang attacks.
Olivia was one of three people shot dead in the space of a week in Liverpool amid a rise in gun and knife crimes.
Council worker Ashley Dale, 28, was shot in her back garden in another part of the city in what police believe may have been a case of mistaken identity, while 22-year-old mechanic Sam Rimmer died after two people opened fire as he stood in the street with friends.
Investigators have identified the two guns used in the shooting – a .38 revolver that killed Olivia, and a Glock-type self-loading 9mm pistol that has been used in three attacks in Dovecot over a two-and-a-half-year period.
Anyone with information is asked to DM @MerPolCC or contact @CrimestoppersUK on 0800 555 111.
