Good find. I wonder if his mother was aware of that post or had heard him making statements to that effect. That would explain her remarks but also bring up questions as to whether she did anything to try to stop him (Baker Act him?) or alert authorities that he might be dangerous. Tough situation for a mother to be in though.
What’s odd is the police didn’t find his mom before she woke up and heard the news. He must be not talking at all, or heavily sedated and asleep.