Rudy Guede did not confess. He admits he was there, on an impromptu date with Meredith Kurcher, heard a commotion while he was taking a dump, disturbed the killers, who ran for it. He pled guilty for a shorter sentence. He chose a fast-tracked trial and was originally sentenced to 30 years, reduced on appeal to 16. Knox and Sollecito were also convicted and got longer sentences than Guede because they went to trial. They were but were later freed on appeal.
I’ve no idea what the truth is but your summary is inaccurate.