The Double
Richard Gere played a retired CIA operative working with a rookie FBI agent to solve the murder of a US senator caused by a Soviet assassin. Guess who the assassin was…
In The Nine Tailors by Dorothy L. Sayers, you could consider that the amateur detective who is the main character of the story is one of those responsible for the death.
It’s arguably the case in Face/Off.
That one had some interesting developments: The murderer was literally washing the victim’s blood off the murder weapon when the authorities showed up. And he actually thought he had been caught, it wasn’t until they brought him in to meet the West Point Superintendent that he realized they were asking him to investigate the murder.
At which point he used his position as the investigator to both cover his tracks and commit a second (and possibly a third?) murder.
“A Tattered Web” is a 1971 TV movie starring Lloyd Bridges, Frank Converse, and Broderick Crawford. Bridges plays a detective who accidentally kills his son-in-law’s (Converse) mistress, then gets assigned to the case. Not a whodunnit, so it might not exactly fit the category.
Speaking of stuff that doesn’t quite fit, but might be worth a mention: CHICAGO has defense attorney Billy Flynn try his best to get his client acquitted right after a fellow-prisoner witness took the stand at the murder trial to read out some damnably incriminating stuff from the defendant’s diary: that, no, it wasn’t self-defense, but murder!
Like you’d maybe expect a lawyer who’s only just now learning of all this would, Flynn starts asking the witness question after question — you know, as if in hopes of discovering whether his client has been framed? — so, hey: did the prosecutor grant you immunity for some other crime, in exchange for your testimony here today? Uh-huh. Say, read some more entries out: do those sound more like the simple words the working-class defendant has used during this trial, or more like (a) the legal jargon that a fancy lawyer would use? Specifically, (b) words that we’ve all heard the prosecutor — who, come to think of it, has had a copy of my client’s handwriting since before this trial started — use? Under penalty of perjury: did you personally find this diary, or was it just handed to you by someone who uses fancy legal jargon? Oh, wait: by someone else, who got it handed to them by someone else?
Once he gets all the right answers, the defense simply rests; the jury, convinced, finds his client to be Not Guilty. Yes, his client had been framed for murder. Yes, by a lawyer who had a copy of her handwriting and forged those diary entries. Yes, by Flynn.
Not the detective, but I have recently read mysteries in two different series where the murderer was the local coroner.
Handy that.
There’s a classic film where a movie star (a) breaks down in tears upon learning what his wife has been up to behind his back, and then (b) goes on the run when the guy that his wife has been up to things with is then found murdered; a lawman promptly shows up — making his debut by showily spotting that someone is trying to surreptitiously remove evidence from the scene of a crime — and delivers some helpful exposition, about having already gotten some useful information from someone, while questioning someone else. And, one reliable tip later, he arrives at a bar: upon getting stonewalled, he switches tactics to offering a reward; upon still getting stonewalled, he points out a clue that no one else seems to have noticed and switches to a ploy that he figures will get the fugitive to break cover; a guy at the scene has just enough time to express some skepticism before the investigator’s knowledge of psychology proves to be entirely solid, such that the actor on the run stands revealed and gets taken into custody.
The actor has of course been hunted down by the actual murderer, who framed Roger Rabbit.
Some advice on this (in spoilers, because the advice gives away which play it is):
If you ever go to London, watch the West End production. It’s the world’s longest-running show - the original production of 1952 is still on (albeit obviously with new different actors) and performed every night. At the end, the actors come on stage and ask the audience to promise not to reveal the final plot twist. It’s all very cosy and homely.
And two more fun facts about it: The copyright to the play was given by Christie to a grandson as a birthday present, and he is still collecting royalties. And there has never been a Broadway production of the play, nor one in Australia, because Christie at one point mandated that it should be performed there only once the original West End production ends - and it hasn’t ended yet.
Nor made into an English-language movie, for the same reason. It has been filmed in Russian and Hindi, but cannot be filmed in English, until the West End production ends, or, more likely, when the copyright expires.
Nevermind
I vaguely remember a very old story about a serial killer and the inspector (French) investigating it. The inspector is famous due to his many previous successes. Finally, the scene of one of the murders has a clue: a shoe print with a unique feature. It turns out the inspector recognizes it because he has exactly the same shoe, custom made due to a missing toe or something. Of course he turns himself in to his superiors. I’m not sure about what follows. IIRC it turns out he’s a sleepmurderer (not a sleepwalker) and forgets what he did at night. He was found guilty but sentenced to life in prison only at night because he wasn’t dangerous during the day.
I remember reading about this one in The Book of Lists. The inspector was actually in socks when he was sleepwalking (and committed the murderer); that’s why the missing toe was so prominent. He found his socks covered with sand, test-fired his own weapon to match with the bullet that killed the victim, and then turned himself in. I think he was found not guilty of murder but was required to have some special safeguards in place at night (I forget what, exactly).