While the shooter may have shot people before thereby considered a ‘pro’, I doubt his experience. A real pro would have used a revolver so no spent shell casings could be found at the scene. Empty shell casings sometimes have fingerprints on them from preparing the ammo and/or from the loading of the gun.
In this case the casings are reported to have the words "Deny", "Defend", "Depose" on them. Could be an anti-insurance antifa type. Or a hitman posing as one as a means of creating a false lead. Maybe just a disgruntled employee losing his job to India.
Uh - it’s nearly impossible to suppress the shots on a revolver. That gap between the cylinder and the barrel.