There's nothing to stop anyone from claiming anything they want. It's word against word. There is no neutral authority that's going to investigate during the middle of a war.
The only way to prove a war crime (like killing civilians), is documented evidence and/or testimony from fellow troops.
Russia has such a history of making fake videos that hopefully any video "evidence" presented by them is immediately taken with mountains of salt anyway.
The only way to prove a war crime (like killing civilians), is documented evidence and/or testimony from fellow troops.