Hells Angels bikie Zeljko "Steve" Mitrovic

Killed: Zeljko Mitrovic. Photo: Supplied

Michael Basanovic isn't exactly a loyalist when it comes to his patches.

A member of the Bandidos bikie gang first, he then patched over to the Rebels, before switching again, this time to the Hells Angels.

But threats and questions over his divided loyalties may have ultimately led him to kill one of his chief accusers.

Michael Basanovic

Chief suspect: Michael Basanovic.

Mr Basanovic is the chief suspect in the January killing of high-ranking Hells Angels bikie Zeljko ''Steve'' Mitrovic, who was gunned down at his Wetherill Park business.

But he has gone to ground, and police on Sunday added him to the state's most wanted list.

Before the fatal event earlier this year, Mr Basanovic had been kicked out of the Hells Angels, having incurred the wrath of senior bikies over his divided loyalties.

''There's nothing worse than an ex-member,'' acting Homicide Squad boss, Detective Inspector Mick Sheehy, said last week.

Police allege Mr Basanovic was among a group of about seven people they have now identified who arrived at Mr Mitrovic's Dynamic Transport business, with the senior club member intending to pull Mr Basanovic into line.

An initial heated argument is understood to have taken place - caught on CCTV at the Mitrovic business - before a smaller group, including Mr Basanovic, followed Mr Mitrovic into his office.

Minutes later, one allegedly pulled a gun and shot Mr Mitrovic dead.

A co-worker caught in crossfire was shot in the arm.

Detective Inspector Sheehy said police would not confirm whether Mr Basanovic was the trigger-man, but said: ''He's a principal in the offence.''

Strike Force Lambourn has issued arrest warrants for Mr Basanovic, and are asking anyone who may have seen him to contact police urgently.