Before the invasion, the Ukrainians were working on the Grim-2 missile, and even paraded launchers for it, possibly loaded (and possibly fake). Ukraine has plenty of engineers, including missile engineers.

So I'll hold to the Grim-2 theory.

Sabotage seems very unlikely, given the locations of two of the craters, and the simultaneous or near simultaneous two major explosions, which were too far apart of one to have caused the other.

Some day we'll know whether that's right, I suspect.