Haven't watched it, but I know the general premise.
The first conviction is a common problem with verdicts awarded in the 70s-90s. DNA evidence didn't exist or was primitive but the media was already in the business of stirring up civil unrest over unsolved crimes. I worked on the West Memphis Three case, which involved the conviction of 3 teenagers for the murder of 3 boys. The 3 men were incarcerated for 17 years before being released because new DNA tech was about to clear their names.
The second charge appears to be better supported, even if the admissibility of the confession is questionable. I got the impression that the title "Making a Murderer" is really a nod to the fact that the first, wrongful conviction placed a man in prison for enough time that he became a murder as shown by his alleged actions after release.
But there are enough things handled poorly in the second investigation and a serious conflict of interest is present which creates a perfect storm for theories.
Crazy stuff.