Well blame is a tricky word, and I'm sure he did not personally authorize the attack or had any say in it, but it is quite indisputable that he has been a huge factor in propping up Putin for the last 20+ years.

Is it? My understanding is that he completely peaced out of Russia shortly after Putin came to power and has been uninvolved in Russian affairs for ~15 years.

Putin literally became president under his recommendation to Yeltsin. When Putin was warring with the oligarch class and billionaires like Berezovsky, Gusinsky, and Khodorkovsky were imprisoned/killed and their assets seized, Abramovich kept hold of his wealth and influence. He was the one who hand picked Medvedev as Putin's successor in 2008. There are regular articles in the news about his meetings with Putin and exchange of lavish gifts. They are said to still maintain a close friendship.

It's hilarious that people are buying his PR transformation into some kind of philanthropist. Guy was and is rotten to the core.

Might as well say entire Brits prop teflon PM to kill Libyans and Syrians. Let's be honest here, you just don't assign guilt simply by association. Hitler did that. We all are better than that.