LONDON Detectives arrested four more suspects on Friday over the murder of 11-year-old schoolboy Rhys Jones, Merseyside Police said.
Two men aged 20 and 24 and teenagers aged 16 and 17, all from Liverpool, are in custody and are due to be questioned later.
Eleven others have been arrested over the murder. Seven have been bailed and four released without charge.
"Arrests made so far are based on consistent information from callers and round-the-clock inquiries," said Assistant Chief Constable Patricia Gallan. "All individuals arrested so far are absolutely critical to the inquiry."
Rhys was shot dead outside a pub in the Croxteth area of Liverpool last week.
Detectives renewed appeals for a witness who may hold vital clues to come forward.
The witness rang the Crimestoppers hotline on August 24 with information that could be crucial in finding the killer.
"The information to Crimestoppers was significant, but we now need to speak to the caller directly," said Detective Superintendent Dave Kelly. "I would appeal to this person to make direct contact with me."
Police said only that the witness saw someone with a mobile phone. It is the second public appeal to the caller. On Wednesday, Kelly said the witness was "very brave".