In reality, Glossip admitted he tried to cover up the murder. He knew where the body was, but pretended to help the search. Apparently, he had planned to help the murderer cut the body up and dissolve it in acid.
Is he guilty of "masterminding" the crime? That's the part where they only have one testimony and would seem uncertain. Was he involved in the crime? Without a doubt, by his own admittance! He's not innocent. He might be innocent of the aggravating factor of having hired or killed for remuneration but he's not innocent of the murder.
You'd think sites would spend a few minutes reading the court papers on this. Or not, because it doesn't present a nice case. "Don't kill this accessory to murder, just imprison him for life!" "He's innocent of hiring a hitman, he only wanted to aid the murderer!" -- I guess that doesn't have a nice snazzy line to parrot.