Three men are still being questioned over the fatal shooting of Craig Barker close to his home in Everton.
Mr Barker, 19, was murdered when a hitman sprayed a car he was in with bullets.
A 38-year-old man from Luton was arrested during a police raid in Huyton on suspicion of murder, and a 46-year-old man from Huyton and a 44- year- old man from Kensington were arrested on conspiracy to murder.
Merseyside police Chf Supt Mike Langdon said: "We are making significant progress in relation to serious crime cases in the area."
The murder of Mr Barker on Robson Street in April caused a gang war.
Days later Michael Singleton, 19, was shot dead in a house on Wykeham Way, Kirkdale.
The third murder came when Mr Regan, 36, was gunned down as he walked towards his car outside the Clean Machine car wash.
As the violence erupted police launched a series of special operations to end the feud and vowed to put those involved behind bars.