https://rumble.com/vzj5jh-ukraine-mariupol-residents-speak-a...
Sad how you still haven't learned after Russia repeatedly lied to you about how it wasn't going to invade Ukraine.
"Mayor Anatoly Fedoruk, "hundreds of Russian soldiers" were also among the bodies" - so you will also expect hundreds of dead Ukrainians who fought to be buried in the mass grave. That is not a "massacre", that would be war.
We know the media constantly lies about mass graves and what they are, see the Canadian schools or New York and Hart Island.
What they do seem to have evidence of is very bad for Russia. So Russia lost control of the troops in the area. It should have not happened or should have been cleaned up. So far Russia seems to have structurally failed everywhere, so I'd expect more of this.
There seems to be no evidence Chechens were in the area. That would be an alternate explanation of why Russia couldn't control these troops.