With recent outburst of Wagner chief against the Russia defence chiefs in Moscow and threat to withdraw his men from the frontline on May 10th few days to the attack on Moscow/ Putin's residence. From my view they (wagner) are behind the attack. In his words he talked of the defense chiefs being in their offices eating fat while leaving them in the frontline with no ammors to die. And from another view, it will take an insider someone who understands how air defence systems works in Russia perfectly well to attack it with drones, not to talk of getting to Putin's residence/ Kremlin with two drones undetected before detected. Because its difficult to drive a drone from ukraine or america to moscow undetected with the level of defence system in Russia. An experince insider involved and that points at Wagners.