A drone leaves all that bomb trace leaves and more - its construction, hair skin and dna traces of the builder, even its radio control details. So its not perfect; its more like leaving the rifle at the scene.
And the idea that shooting a gun brings down some hailstorm of official response is myth. Fire a gun in most places and ... nothing will happen. Folks will rush to the scene of any murder, but will only find the sniper's location after hours or days of investigation. It won't be like the NCIS show where the investigator glances around and says 'must have come from that rooftop; its the only secure sniper post in a half-mile!' You can shoot from nearly anywhere with line-of-sight, from the partly-open door of a parked delivery van, without much risk of discovery.
And the idea that shooting a gun brings down some hailstorm of official response is myth. Fire a gun in most places and ... nothing will happen. Folks will rush to the scene of any murder, but will only find the sniper's location after hours or days of investigation. It won't be like the NCIS show where the investigator glances around and says 'must have come from that rooftop; its the only secure sniper post in a half-mile!' You can shoot from nearly anywhere with line-of-sight, from the partly-open door of a parked delivery van, without much risk of discovery.