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.