Former Rebels bikie boss Nick Martin killed in front of hundreds at WA motorsports event
A young boy and another man seated nearby were also wounded in the shooting.
WA Police were called to the Kwinana Motorplex after reports of a shooting just after 8.30pm yesterday.
The motorplex had been hosting its Outlaw Nitro Challenge, attracting families including children to watch nitrogen-fuelled dragsters race.
The three victims were treated by paramedics at the scene, but Mr Martin did not survive his injuries.
The other man - a 31-year-old patched Rebels gang member - was taken to hospital by ambulance to be treated for gunshot wounds.
An five-year-old boy, who had been seated on an adult's lap next to the bikies, was treated by paramedics for a "minor wound" but didn't require hospitalisation.
The boy was not related to either of the two bikies but was there with his parents, according to WA Police Commissioner Chris Dawson.
The commissioner said the boy was now at home with his family and was "in good health in terms of his wound".
"The community is justifiably outraged at this type of violent criminal behaviour in a crowd in Western Australia," Mr Dawson said.
"This is not the Western Australia that we want to live in."
He said police would be "relentless" in their pursuit of the shooters, as he called on any attendees with information or vision of the incident to provide it to police.
The police commissioner said police were on high alert for retaliatory attacks following yesterday's shooting.
However, the Gang Crime Squad wasn't focusing solely on any particular gang, Mr Dawson saying they would be investigating "the whole criminal fraternity".
"We all must be outraged by this violent criminal behaviour; in a crowd, an eight-year-old boy, who has received – fortunately – superficial wounds," he said.
"These criminals don't stop and have regard for human life.
"The fact that this shooting occurred in a public place with many innocent people around including children shows the nature of these violent criminal gangs."