“We lost one of the best people ever,” Shane Told, vocalist for the Ontario post-hardcore band Silverstein wrote in an Instagram story. “I watched Dave go from drummer and merch guy to entrepreneur and one of the most important people in the industry. But along the way he was first and foremost a friend.”

Eight people in the Murphy Canyon neighborhood – a military housing community – were injured, including two treated for minor injuries at the scene and six others who received medical attention, poli...