There's an article in the Age describing the sentencing for SH's first murder, stating that the judge took into account his dependence on amphetamines as reduced moral culpability. In 2002 he was charged with possessing amphetamines (apparently he was a delaer too) while on parole... Makes sense to me; this guy obviously has a problem with this drug which reduces people's inhibitions. Clearly a factor in this murder. Maybe SC was a customer or co-user, going by other people's statements and CS's statement on SC's profile pic. Hmm... Explains a lot to me.
edit: someone on fb mentioned that TB is/was a dealer too, they had apparently bought off him a few years ago in the Ararat area. So it looks like 'da gang' was probably a small-time amphetamines ring, IMO...