''The Thin Blue Line'' is a 1988 American documentary film by Errol Morris, depicting the story of Randall Dale Adams, a man convicted and sentenced to death for a murder he did not commit. Adams' case was reviewed and he was released from prison approximately a year after the film's release.

The film argues that David Harris, who Adams was with that evening, actually committed the murder, while the justice system conspired to convict Adams for the crime due to his outsider status as well as his age (Adams was nearly thirty, while Harris was still a teenager). Unlike other documentaries, the film eschews voice-overs and text, instead relying almost completely on talking head interviews and reenactions of the murder, in effect letting the evidence speak for itself.

''The Thin Blue Line'' has been lauded since its release, and is considered by many critics to be among the greatest documentaries ever made.

!! This film provides examples of:

* AmateurSleuth: Emily Miller, one of the "witnesses" who put Adams behind bars, admits that she always wanted to be some investigator's wife. She ends up coming off as not only nosy but starved for attention, and also greedy for the reward money that would come with help solving the crime.
* BadCopIncompetentCop: On the incompetent side, Teresa Turko really doesn't come off as the brightest cop in the force. She apparently breaks procedure by sitting in the car drinking a malt instead of being in the appropriate position for a traffic stop, which makes her fail to react to the shooting in time, get a license plate number or hit the fleeing car. She wastes manpower by giving the wrong model of the car and gives unreliable testimony after being coached by Internal Affairs (she originally stated the shooter was wearing a jacket with a fur-lined collar, which Harris was wearing; after coaching, she claimed the shooter had long, bushy hair, as Adams had). On the bad side, it becomes increasingly clear that there was little short of a conspiracy against Adams, as Adams was an outsider to the area even though he had no history of violence whatsoever, while the law enforcement was reluctant to sentence the teenage Harris to life in prison despite his numerous violent crimes.
* BittersweetEnding: Adams is eventually freed, due in large part to the documentary; however, he still had to serve all that time for a crime he didn't commit, he wasn't paid a cent for his false imprisonment, and he ended up in a legal battle with Morris over the rights of his story.
* CopKiller: The murder in question is that of a police officer. Harris brags about being a cop killer to his friends back home, which Morris uses as evidence pointing towards Harris's guilt and not Adams'.
* CopKillerManhunt: After the car that housed Wood's killer was reported as being a blue Vega, the police searched just about every blue Vega in the area, and people with Vegas in different colors requested they be officially cleared just so they wouldn't be stopped anymore. After Teresa reports under hypnosis that it was actually a blue Comet, one of the policemen bemoans all the time and energy wasted searching for the wrong car.
* EvilIsPetty: The final interview with Harris suggests that he blamed Adams for the crime solely simply because the latter hadn't offered him a place to sleep in his motel, forcing him to sleep in the parking lot.
* FalseConfession: Adams signs a confession that doesn't even incriminate him, but leaves enough holes to make him look suspicious at best and guilty at worst, and is reported as being a confession to the murder.
* FreudianExcuse: Harris partly blames his actions on his father, who treated him more neglectfully after Harris's brother accidentally drowned when they were kids.
* InkblotTest: Adams is given a variation to test his mental state. Though none come off as being particularly useful, he completes all the tests as any sane person would, yet the psychiatrists accuse him of being a remorseless murderer fit for the death penalty anyway. Adams' attorney dismisses the psychiatrists as quacks who argue that ''everyone'' is fit for the death penalty.
* InternalAffairs: Adams argues that they coached Turko into changing her testimony to incriminate him instead of Harris, who fit her original description.
* LongerThanLifeSentence: A FreezeFrameBonus on a list of convictions shows the famous 5005-year sentences for Woodrow and Franklin Ransonette for their 1973 kidnapping of an heiress (which were later reversed).
* PlethoraOfMistakes: When not being maliciously biased against Adams, nearly everyone in the prosecution acts foolishly at one point or the other, such as unquestioningly believing some completely unreliable witnesses.
* TheSociopath: Adams is falsely labeled as one of these for showing "no remorse" for the crime; his DA argues that he naturally wouldn't feel remorse for a crime he didn't commit. Harris, on the other hand, genuinely seems to feel no remorse for any of his crimes, as noted by even his friends.
* TitleDrop: Spoken during Mulder's prosecution. Mulder meant it sincerely, while Morris uses it ironically, questioning the infallibility of those who uphold the law.
* WhamLine: The final interview with Harris is one WhamLine after the other, where Harris all but directly admits that Adams was completely innocent of the crime and he falsely accused him out of [[EvilIsPetty pure spite]].