Jessica Fletcher is a KiraShe sets up the murders and covers her tracks by covering over the Death Note and saying she's writing murder mysteries, and is able to solve the cases because she set it up that way.
Jessica Fletcher always gets confessions offscreen from the killers, verbatim, before she tells everyone else.She knew exactly what a murderer and his girlfriend had said while they were alone in a wide field.
Jessica Fletcher has ghosts help her solve crimesPossibly those of the victim or previous murder victims.
Jessica Fletcher has the entire Northeast bugged.Sheriff Tupper set it up, but hasn't the slightest idea what to do with it. It's all highly inconspicuous for the era. And when she moves to NYC in a late season, she taps into their security with her new word-processing computer.
Jessica Fletcher killed all those people and pegged the blame on others to make herself famous
Jessica Fletcher is the Anthropomorphic Personification of Murder.She naturally creates a murder-field that increases the premeditated crime rate 1000%, often retroactively, wherever she travels. Her kindly old lady facade is a ruse to lull the unwary — Obfuscating Stupidity.
Jessica Fletcher is a Reaper with guilt issues regarding her job.She deals with them by making sure that the Reapee's killer is caught.
Jessica Fletcher is related to Kudo Shinichi/Edogawa Conan of "Detective Conan."
All the murders around Jessica Fletcher are orchestrated because of Jessica Fletcher.Someone or something is ensuring murders continually occur around Jessica Fletcher.
Cabot Cove is Evil.Whether Jessica Fletcher realizes it or not, something about Cabot Cove compels people to murder. Cabot Cove's two percent murder rate is unnaturally high not to attract attention.
Jessica Fletcher killed her husband.Seth Hazlitt helped cover it up.
Jessica Fletcher is an earlier incarnation of Suzumiya HaruhiShe was a murder mystery writer, so obviously she subconsciously wanted to have lots of mysteries to solve. So being God/a higher stage of evolution/whatever the heck Haruhi is, she fashions the universe around herself to give her mysteries. When she finally passed away, she was reborn in Japan and continued her insanity.
Jessica Fletcher lives in a Crapsack World where people have anger management problems.That's why so many people are killed - everyone is so Hot-Blooded. Think about it. And because of this, murder is her world's equivalent of jaywalking or theft (petty or otherwise). It's not as serious a it is here, so more people do it.
Jessica Fletcher is immortalIn the unlikely event she didn't commit the murders, she'd have to be.
Jessica Fletcher will be murderedShe's such a good detective, she already knows who the murderer will be, and has already set things in place such that her murderer will confess after the wrong person is arrested at first. After it all dies down, the manuscript of her final novel, to be published posthumously, will be found, detailing all of these events in advance.
The entire series is nothing more than story ideas that Jessica has created for her books.Think about it: She knows ALL of the victims personally...she was only the suspect in a few of the murders but that didn't last....she's able to solve all of the crimes no matter how convoluted solution...and no one seems to comment on the incongruity of an elderly woman being or near the scene of so many murders. Why does this all occur? Because all of the "murders" take place in Jessica's MIND as ideas for new novels.
Jessica Fletcher is in some way related to Richard Castle.Both bestselling mystery novelists who help the police solve murders — and you're telling me there's no connection?
Jessica Fletcher committed all the murders.Chris Hardwick has suggested this, elaborating that the entire series is her hallucinations as she tries to come to terms with the horrible things she's done—Kinda like St. Elsewhere, except with psychological coping instead of autism.
Jessica Fletcher is the leader of an Assassin's Guild.Every time there's a murder, she's on hand to keep suspicion off her underling, who is usually posing as an "old friend" or distant relative, by framing an innocent patsy. There's never any real evidence against the patsies, but they are made to confess or otherwise implicate themselves by intimidation.
Jessica Fletcher is a Reality Warper who feeds on souls.She kills people to devour their souls then warps reality to blame other people.
Jessica Fletcher is a Psychopomp.She doesn't cause the deaths, they would happen regardless. Jessica's appearance on the scene happen because she heralds the victims to the afterlife and resolves them of their issues by solving their murders.
Jessica's books are ghostwritten.In general, the second biggest question of the series is how Jessica was able to write all her novels. The other wiki lists her collection of in-storyline novels sitting at 43 (and since she was promoting the first one in the pilot, that implies 43 novels in 12 years.) That's a staggering output for someone who does nothing but write, but it seems downright impossible for someone who also teaches, travels, and also guides piss-poor police detectives in the right direction when solving the murders of the hundreds of victims who fall like dominoes around her. The possibility remains that, like the Stratemeyer Syndicate, she provides outlines for stories, sends them to ghostwriters (possibly one Donald Bain?), and possibly helps to edit them. Maybe Bain finally revolted and demanded credit for his work, which is why he's now co-author of Jessica's recent work?