Or by the shooter itself. Several things "different" about the shooting of the kid, even though they 'matched' the bullets. The "matted area" indicating shooting from outside a vehicle and not behind much concealment either. The shell casing left behind, whereas in the earlier shootings, no brass was found. And now a Tarot card?
Lots of rifles can fire those caliber bullets. And after impacting the target, identifying the remains of the bullet as coming from a specific weapon, is often impossible.