Ukraine blames Russia and Russia blames Ukraine.
some context:
ruzzia tried its hardest to blame Ukraine. after initially stating "Kyiv did it!!!111", that narrative fell apart: ISIS-K claimed responsibility, uploaded go-pro vids, and made it impossible to deny that they did it. so then the kremlin changed their story: Ukraine didn't do it but "gave support". ruzzia claimed that the suspects were trying to escape to Ukraine and that a "window" has been opened on the UA-RU border to let them through, so clearly UA is guilty! except that 1) the suspect were caught on the road to Belarus, not Ukraine, and 2) the UA-RU border is impossible to cross: you'll hit several checkpoint on the russian side before you get to the border, zero chance a civilan car can just drive through. the border is also heavily mined, no vehicles can pass.
Ukraine "blamed" ruzzia in as much as they've said they weren't responsible/involved, and put forth the idea that it was a false flag operation by the russian security service (FSB). there are a lot of details that make a false flag operation a possible if not likely explanation, chief among them: numerous 911 calls were made but it took almost an hour and a half for authorities to show up - despite having a large base of the national guard (including rapid response forces) located just 5 minutes away. the only logical explanation is that they were told not to respond immediately, because the kremlin wanted a massacre - it would help with the upcoming mobilization and justify additional violence (moscow has a history of doing this - 1999 apartment bombings, 2002 theater hostage crisis, etc.)
after being caught, the suspects were tortured by ruzzian police. one suspect had his ear cut off and stuffed in his mouth. another has electrodes attached to his testicles and shocks applied during interrogation. how do we know this? the ruzzians released videos of them doing this... savages. the electrocuted-balls suspect was later carted into the courtroom unconscious - yet he somehow plead guilty. all 4 suspects showed signs of beating and torture.