In the British crime drama Broadchurch, the killer of the 11-year-old boy Danny Latimer, revealed in the first series, is Joe Miller, who is the husband of Detective Sergeant Ellie Miller. Joe Miller strangled Danny Latimer, and this was discovered after months of investigation in the series. The reveal of Joe as the murderer is a central plot twist of Broadchurch's first series.

The later series of Broadchurch focus on different crimes, including a third series about the rape of a local woman, Trish Winterman, which is solved with Michael Lucas, the son of a cab driver, as the perpetrator.

So, regarding the question "who did it" in Broadchurch, the answer depends on which crime is referenced, but the most famous "it" from the first series is Joe Miller as Danny Latimer's killer.