Detectives probe whether a fly-in-fly-out killer was behind the sniper assassination of a Rebels bikie boss - which happened four days after WA opened its borders to eastern states

Detectives are investigating whether an east coast hitman was behind the gangland killing of a Rebels bikie boss who was shot dead by a sniper in a highly-orchestrated assassination.

Nick Martin was shot in the back while attending the Outlaw Nitro Challenge drag racing event at the Perth Motorplex, Kwinana Beach, at 8.30pm on Saturday - just four days after Western Australia opened its borders to New South Wales and Victoria.

The underworld figure died at the scene in front of horrified families and children, including his own wife and step-daughter.

Western Australia Police have confirmed to Daily Mail Australia they are working with partner agencies in eastern states as they probe the possibility of a fly-in-fly-out killer.

Nick Martin at the Rebels clubhouse. The bikie boss was murdered in public on Saturday in front of his family

Paramedics tried to save bikie boss Nick Martin as shocked families watched in horror after the shooting on Saturday night. Pictured: paramedics at the scene on Saturday

While overnight raids were carried out by heavily-armed tactical officers at properties linked to the Rebels, Mongols and Hells Angels - one of Australia's foremost experts on outlaw motorcycle gangs said the brazen attack does not have any of the hallmarks of 'bikie activity'.

'If this was a dispute between clubs or an internal conflict within a club, it wouldn't have happened this way,' Queensland University of Technology associate professor of criminology Mark Lauchs told Daily Mail Australia.

'It would be a much more public confrontation or they would have ambushed him. It's not common to kill people in other OMGs over what they call - club business.'

Prof Lauchs said bikies don't typically have the marksmanship skills to take a shot from such a great distance - especially in front of bystanders.

He suspects a professional shooter from another organised crime outfit carried out the attack.

'Based on other cases in Australia where someone has been intentionally killed and not accidentally killed in a drive-by - it's usually associated with organised crime rather than OMGs,' Prof Lauchs said.

'It would be very unusual for an OMG to carry out this kind of attack.' 

One of the possible shooter locations at the Perth Motorplex. A long shot would indicate a sniper, experts say

Although bikie chapters mostly operate separately and rarely bring in members from other states, that's not the case when it comes to more traditional Australian organised crime.

'Historically if you are in organised crime in Australia and you want to do a hit on someone, you would bring someone from interstate who can come and do it and then leave,' Prof Lauchs said.

'You fly someone in from outside the jurisdiction so they can get up and leave for the purpose that local police will never catch them - simply because they are not looking for this person.'

Even if an interstate killer is captured on camera, local police will have a tough time trying to identify the suspect - as investigators will need to undertake the painstaking process of liaising with other law enforcement agencies across Australia.

'Going back 100 years, this has been the classic organised crime method of doing things,' Prof Lauchs said.

Western Australia finally reopened its borders to New South Wales and Victoria on December 8 after being closed to non-citizens and non-residents since March due to the coronavirus.

Amanda Martin's Facebook page is flooded with photos of husband Nick (pictured together)

'There must have been a shortage of organised crime hits during Covid because they couldn't fly interstate,' Prof Lauchs said.

'So I wouldn't be surprised if there was a connection between the timing of the borders opening and this killing.'

The brazen nature of the execution which also injured another Rebels gang member and a five-year-old boy, who was sitting on his parent's lap nearby, has authorities desperately seeking answers. 

On Tuesday police offered a $1million reward for information that leads to an arrest.

As the hunt for the gunman continues, Martin's grieving family has hit back at claims by WA Police Commissioner Chris Dawson he had recently 'lost his status' in the Rebels bikie gang.

His daughter Tia Martin, 22, insists he wasn't stood down by the club but confirmed he was legally barred from communicating with Rebels members and 'would have gone to jail' if he was caught associating with them due to an ongoing court case.

Martin's step-daughter Stacey Schoppe tried to revive him at the scene

'He was on charges and was on non-association and was not able to talk to anyone in the club in months,' Ms Martin told The West Australian.

'(His assassination) definitely did not come from within the club. We are family.'

Reports, denied by his daughter, suggested his shooting was in retaliation for alleged problems he had in the club.

Daily Mail Australia is not suggesting any associate of Mr Martin's was responsible for his death.

Prior to his death, Martin was a well-known identity in Perth's underworld and had survived a series of attacks.

He was shot in the arm while arriving at his Balcatta home, in Perth's northern suburbs, in March 2011.

Emergency services at the Perth Motorplex on Saturday night shorting after he was shot in front of horrified families

Police slammed bikies on Monday saying they take their violence into public areas putting everyone at risk. Pictured: the scene on Saturday after families and bystanders had fled

Pictured: Perth Motorplex at Kwinana Beach where the shooting occurred on Saturday

At the time the Rebels were locked in a feud with the Rock Machine Gang and its member Benjamin Spikes was convicted over the shooting.

One year later Martin's Balcatta home was the target of another attack and his car was firebombed.

Martin was also allegedly involved in a brawl with a Hells Angels bikie at The Sandbar, in Scarborough, on November 24.

Security cameras filmed two men speaking with each other and shaking hands before a fight broke out involving staff and patrons at the trendy beachside bar.

Pub goers could be seen in the footage running away from the scuffle as furniture was tossed around the bar during the violent fight.

Daily Mail Australia is not suggesting the two incidents are linked.

Martin's stepdaughter Stacey Schoppe (pictured together, with her mum, left) was just centimetres away from the chaos and was nursing a friend's young son when she started to realise he had been shot