Putin said he won't invade. Then he said Kyiv will fall in three days. Then conducted fake referendums, "annexing" territories he doesn't control. Izyum was declared a part of Russia forever from now on, and that "forever" lasted two days. So, this "doing what he says" doesn't quite check out.

As for casus belli - against whom exactly? And why would Russia need any casus belli?