Ukraine
Again though, how does Ukrainian drones even travel that far. Drones do have a limited range and traveling hundreds of miles without getting noticed or shot down makes little sense.
I'm not disputing the rhetoric, but Ukrainian psyops is a thing too.
The first explosion occurred at ground level and I still think that was probably a backpack or pressure cooker bomb that was set on the sidewalk next to the building. It was intended to make the loudest brighest bang.
The following two hit higher up on the sides of the buildings, and probably were drones. They packed a whole lot less punch.
Those building weren't harmed that badly, not even the one with the at ground explosion. The type of engine that was found at the base of one of the second two explosions are of the kind like the drones the Iranians are building for the Russians. However there are Ukrainian drone designs using an engine like that as well.
It is apparent that the engine was set up as a pusher engine from the rear, not a pulling engine from the nose because the prop survived mostly intact. Since the engine was a smaller two cylinder, I would think the max payload was 20 pounds of explosive at most. Probably less.
They could have the range to have gotten from Ukraine, however it is more likely that they were launched from the outskirts of Moscow.
Perhaps the Russian legion or Ukrainian special forces who infiltrated Russia in a Scooby Doo van. Four guys and one van could have done it. Set up two drones for launching out of town, then one guy drove the van into town with a backpack bomb and set it.
Then the guy in the van returned and picked up the three who launched and flew the drones. They achieved a lot with very little buck.