The criminal justice system is many things to many people. To some, it is a venerable institution, trying to balance many competing interests and points of view. To others, it may be the instrument of oppression. But the longer you look at the system and the more cases you examine, the more you realize that it is exceedingly prone to error.
This point is raised in an interview with Errol Morris, who made a remarkable documentary in 1988, The Thin Blue Line. That documentary detailed the arrest and prosecution of a man charged with killing a police officer. He was convicted and sentenced to death.
After the movie came out, and the errors of the prosecution were made clear, his sentence was overturned and he was released. In an interview discussing the fascination with "true crime" stories and the Netflix series Making a Murderer, Morris notes that the powerful element of that story is not the guilt or innocence of the individuals involved, but that "feeling of the inexorable grinding of a machine that is producing, potentially, error."
Which is one reason why when you have been accused of a crime, you want a defense attorney who will aggressively challenge the evidence and other "proof" that the police and prosecution claim shows your guilt.
Many cases are dismissed for lack of adequate evidence, and a careful investigation of the situation can often find that seeming "facts" are merely a house of cards, with uncorroborated statements bolstering other similar statements.
A rigorous examination of the police investigation may also show that there may not have been much if any, real investigating going on. Investigations may be poorly conceived and poorly executed, and police may make an error early in the process, compounding the flaws of the prosecution.
Source: slate.com, "What Errol Morris Thinks of Making a Murderer," Isaac Butler, January 27, 2016