Jackson attacked the prosecutor for having no better reason for wanting to try the three men again other than "his personal opinion of rampant, evil, satanic-worshipping, Stephen King-reading, black tee-shirt-wearing guilt".
The men were released on the basis of a legal manoeuvre know as an "Alford Plea", under which a convicted person accepts the original convictions will stand without attracting a claim for compensation.
The alternative, he wrote, was that the men would wait years for a retrial.
He particularly expressed sympathy for Echols, who had spent the past 18 years on death row locked in a cell without seeing outside.
"He has not seen sky for over 10 years. He has not had sun on his skin for over 10 years. He is shackled hand and foot whenever he leaves his cell. His eyesight has deteriorated."
Jackson said the case was an appalling miscarriage of justice which had allowed a triple child killer to walk free for the past 18 years.
He said new DNA evidence and testimony that previous witnesses had lied under oath proved the men were innocent.
Hundreds of Jackson's fans "liked" his post with some suggesting it would make a good movie.
