Police have laid murder charges after earlier arresting seven people in relation to the deaths of two boys aged 12 and 15 in Melbourne's outer west.

Dau Akueng, 15, and 12-year-old Chol Achiek were killed on their way home from basketball in the suburb of Cobblebank earlier this month.

Authorities at the time described the scene as "one of the worst" knife crimes they had seen.

Homicide Squad detectives today arrested three men and four teenage boys as part of their investigation.

Warrants were executed at about a dozen properties across Melbourne's outer west and north at 6am this morning with assistance of the VIPER youth gang taskforce.

A 19-year-old Thornhill man, two 16-year-old boys and a 15-year-old boy have been charged with the murder of 15-year-old Dau Akueng.

A 19-year-old

See Full Page