"Culpable homicide is not murder if it is committed without premeditation in a sudden fight in the heat of passion upon a sudden quarrel, and without the offender having taken undue advantage or acted in a cruel or unusual manner"
In this case when the gang called other members, armed themselves and with numbers, there is clear planning and therefore premeditation. There is no "sudden" quarrel.
Unfortunately the Police will never pursue the murder charge when the assailants and the victims are secret society members. The only exception was a case involving army boys with SS background from armour that killed another SS member in Kallang Park. All kinds of reasons have surfaced including the inability to identify the person who delivered the fatal blow, cut or insertion. They will end up with 7 years jail but come out after 5 years. They then wear a badge of honour claiming they have killed someone and are some big dog. If you notice despite the violence, SS members will never kill a non SS member because they know the death penalty will kick in. SS members will also attack in large numbers and will continue to slash, stab and cut even when the victim is obviously dead. The next day, they will voluntarily surrender themselves.
A precedent has been set and no one seems to care.