Considering the value of Azov being alive to UA and RU sides, both claims sound ridiculous to the point of being laughable. So most likely this was an accidental attack. As these things go, like with MH17, one side will try to do everything to investigate and drum up as much attention as possible, and the other side has no option but to just blatantly deny everything and try to make it go away ASAP.
It's even more ridiculous to say it was accidental attack.
The captured Azovites are still highly valued for exchange, because at large in Ukraine they are apparently still considered the elite and there are many more of their fighters and supporters at large who are pressing the Zelensky government to exchange them in the very first place.
For the Zelensky government, for which victories on the information front are much more important than real ones, it would be better if the Azov people did not surrender, but died the death of the brave as martyrs. Therefore, on the one hand, Kyiv exchanges part of the soldiers, and on the other hand, instead of Russia, it may well seek to complete its plan to glorify the prisoners from Azovstal by completely destroying it. Moreover, as mentioned above, such attacks may be designed not only to intimidate witnesses, but to reduce the desire of Ukrainian soldiers to surrender into Russian captivity.
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I'm projecting that a lot of people who are currently Ukrainian POWs of the Russians will ultimately be re-armed and re-trained by Russia and will ultimately be fighting Poland when the Ziocons fuse the two countries.
I'm expecting that some of the 'Nazis' are so because of some intensive and invasive psychological techniques that can probably to some degree be reversed. As they said, rightly enough, the Ziocons and everyone else loves them because they are highly effective at causing up trouble. Like it or not, the 'force multiplication' effects of terrorism are significant. The problem for 'Nazis' is that when their usefulness to the Ziocons is done they are far far more likeable and less dangerous as dead Nazis. My guess is that that is the main reason behind the POW camp attack.
An alternate hypothesis is that the Russians wanted to test out one of the American HIMARS systems they bought from the Ukrainians and did a 'false flag' on the POW camp to kill several birds with one stone. I personally would find that quite amusing, and very fitting, but I doubt that it is the case.