The investigation comes after the ex-Knights player spent two days in intensive care in December, after a near-fatal drug overdose at a party hosted by former Blues legend Willie Mason’s brother.
Mason, 40, was charged in late December with drug supply offences unrelated to the Mullen overdose.
Mullen, who spent weeks in rehabilitation before relocating his family to Newcastle, has not yet been charged, but NSW Police have released a statement indicating imminent arrests.
“Strike Force Castlestead was formed in September 2018 to investigate and dismantle an alleged drug supply syndicate operating across the Newcastle City and Lake Macquarie Police Districts,” the statement read.
“Since December 2018, five search warrants have been executed by Strike Force detectives and ten people have been arrested and charged in relation to a range of matters including ‘supply a prohibited drug of large commercial quantity’ and ‘knowingly participate in a criminal group’.
“Investigations by Strike Force Castlestead continue and further arrests are anticipated.”
Mullen is currently serving a four-year ban after testing positive for steroid use in 2017.
He scored 29 tries in 211 games for the Knights from 2005 to 2016.