Someone you love has just died in a terrible and, honestly, kind of suspicious way. Better start crying your eyes out right now.
Wait, you say you have a sense of personal dignity and prefer to mourn in private, and wouldn't dream of sullying your loved one's memory by breaking down just in time for the ten o'clock news team to catch it? Or that you're in shock and too bewildered and horrified to do anything but stare blankly?
Look, you're just asking for trouble, pal. We said cry and you'd better turn on the gushers. Because if you don't then you're the killer! And when the case comes to trial six months later you had better still be crying, or the reporters are going to be jabbering about how you sat there "emotionless" during the "most brutal part of the testimony," which is guaranteed to make you look bad even if you aren't actually the one on trial.
This trope has been around on television so long that these days the subversion is at least as common as the trope: the "non emotional" person at the scene makes for an excellent red herring for the first half hour of a crime procedural, but is rarely the true killer because that would be too easy. You can expect the truly guilty person to have had the wetworks on full blast, just as expected, if only to throw off suspicion.
Sadly, this trope in its unsubverted form is still commonly seen in Real Life crime, where not grieving enough in public, not being sad enough, or engaging in necessary unpleasant tasks such as checking on a spouse's life insurance too soon after the death, is seen as evidence of an evil or heartless nature, and therefore guilt.
Shares some similarities with Loners Are Freaks: failure to conform to expected social norms makes you a monster.
Light in Death Note agonizes over whether or not it would be wise to visibly grieve when his father nearly dies. He ends up being a bit hammy.
In a case in volume 16 of Detective Conan, one of the sisters comments on the fact her brother's fiancee (who she dislikes) has barely reacted to his death, insinuating that she was a Gold Digger. Ran runs after the fiancee to give her something she'd dropped, only to find her crying about her fiancee's death alone. It turns out she is the culprit, but it's a lot more complicated than they realized.
In the start of The Shawshank Redemption the protagonist is charged with the murder of his wife. Though there is other evidence that points towards him, what seems to really cinch the case was that he showed no grief, described by the judge as "an icy and remorseless" individual. The fact that his wife was killed along with her lover and that this might take away from the grieving process is never addressed. Sure enough, about two thirds of the way through the movie we find out that he really was innocent.
Subverted in Star Trek VI. Scotty notes that the murdered Klingon Chancellor's daughter didn't shed "one bloody tear" and so she must have been the culprit. Spock points out that that in itself is not conclusive, since Klingons have no tear ducts. Whether Scotty was intending to this turn of phrase be taken literally is not clear, but it's academic in the end: Not only is she innocent, but the same plotters who arranged for her father to be murdered and for Kirk and McCoy to take the fall target her at the climax.
The Deadly Bees: During an inquiry into the death of his wife (by bee swarm), Mr. Hargrove displays less emotion towards his wife's death than protagonist Vicki, who was only a guest and knew them both less than a couple of weeks. This only strengthens the theory that Hargrove set his bees on his wife, whom he openly hated.note In the original novel, he is, indeed, the killer. Here, the real killer was his rival beekeeper, Manfred. Hargrove was merely an innocent Jerk Ass.
Camus' The Stranger sort of messes with this. Meursault's murder trial paints him as an inhuman monster because he didn't act sad at his mother's funeral. It's a bit of a subversion, as he didn't cry because he didn't really care, and he claimed he killed the man because the sun was in his eyes, but his treatment at the trial still fits this trope.
Inverted in the Sherlock Holmes story when a man is arrested for the murder of his father. The fact that he accepts arrest so calmly and he expected it is used as evidence by the police of his guilt. Holmes however points out that it simply shows he was aware of the overwhelming evidence against him and that it was futile to protest; only a guilty man would try and cause a scene.
Lampshaded (of course) in the Discworld novel Night Watch, when Vimes realizes a little too late that not reacting at all to Coates saying he isn't the real John Keel is a dead giveaway.
Played straight in Maskerade, where the murderer is the Deadpan Snarker who makes insensitive but amusing quips about the deceased. It can actually be a bit surprising in a humorous novel where most characters are Deadpan Snarkers at one point or another, but Terry Pratchett has repeatedly commented in his novels how making jokes about killing people, even bad ones, is a telltale sign of twisted morals.
A variation in Madeleine L'Engle's A Swiftly Tilting Planet. Zillah, a Native American woman, doesn't cry or scream while giving birth, due to her culture. The suspicious Puritan townspeople (who already blame her for the current drought) use this as evidence that she's a witch.
In Boston Legal, the victim's girlfriend didn't show any emotion when she saw her hanged, saying only "goodbye". She was considered a suspect by the main characters. It turns out she was only interested in the victim's money, but the act itself was a suicide.
In a CSI: Miami episode they came down hard on the husband of the victim as despite seeming genuinely shattered he had returned to work immediately. This was because he worked in a family business and it was helping him cope with his grief but the CSI's still remarked it pointed toward him being responsible, despite his actions mirroring practically every detective and CSI on TV, including in their show, who has suffered a bereavement without the added reasoning of family being present at the work as well.
Cameron in The Sarah Connor Chronicles has a problem convincing anyone that she didn't kill Riley due to her inability to show anything close to grieving. Well, that and the fact that she's the only one with motive.
Leonard Nimoy does it in the Columbo movie "A Stitch in Crime" (1973). Both Nimoy and Peter Falk (Columbo) act outside their typecast personas in a scene where Nimoy pretends to burst into laughter over the ridiculous idea that he murdered a colleague. Columbo, unusually for him, drops his bumbling policeman act and angrily announces his intent to prove his accusation.
Inverted in Criminal Minds: the team is investigating a series of brutal murders mimicking Native American rituals. Their first suspect is an Apache teacher/activist whom they take to the crime scene under the pretense of asking for his expert opinion. He then proceeds to analyse the grisly scene in a very detached and unemotional manner and comes to the conclusion that this wasn't done by Native Americans. Hotchner then claims his behavior proves he's innocent: a guilty person would have feigned shock and disgust, as the activist himself points out when Hotch tells him that he's not a suspect.
One episode of NUMB3RS has Liz become suspicious when a woman wishes to stay at the FBI office after being told her husband died. This leads to them realizing he was not actually dead.
After Rita's murder, Dexter initially comes off as emotionally detached (particularly in his clinical police call). Quinn (who has a grudge) is alone in finding it suspicious; most of the other people at the precinct think he's just in shock, and Debra worries that he isn't allowing himself to grieve.
The subversion was lampshaded in an episode of Bones in which they interviewed friends of the victim at a fraternity. The frat members who knew more than they were letting on were pointed out by Dr. Sweets because they were too consistent in how sad they appeared (genuine grief varying in intensity and nature from moment to moment) which indicated that they were concentrating on appearing sad rather than actually being sad.
In Home Improvement, Tim's boss and friend Mr. Binford passes away, and when he doesn't seem to be sad enough both Jill and Al get on his case about it. He doesn't see what the problem is if he doesn't get all weepy, but it then bothers him when his son seems to be learning the lesson that Men Don't Cry. For the record, Tim does eventually break down at the funeral.
In Two and a Half Men, Evelyn's new husband Teddy dies before the wedding reception is even over. When she finds him lying dead in a bed (with his pants down and lipstick on his crotch), she picks up the phone... and calls the airline to trade her two plane tickets for a single first-class ticket. The police didn't look too fondly on that.
In Persona 4, Naoki Konishi deals with a variation of this, as the local gossips criticize him for not seeming 'sad enough' about his sister's murder. Reversing this, he criticizes them for acting like they really care about what happened when it's pretty clear they're just more interested in gossiping about it. The climax of his social link involves helping him mourn his loss by providing a truly sympathetic ear rather than acting judgmental and high-and-mighty while offering transparently fake comfort like the gossips.
Played with on Daria: in "The Misery Chick", when ace football star Tommy Sherman is killed when a goal post dedicated to him falls on him, at least four characters (Kevin, Britney, Mr. O'Neill, and Sandy) come to Daria asking for advice on how to cope, since she is reacting to the tragedy with such relative indifference.
Parodied on a Treehouse of Horror episode of The Simpsons when the family hits Flanders with their car and apparently kill him. At the funeral Homer cautions that if they look too sad they'll draw suspicion. So they walk in with wide smiles.
Lindy Chamberlain was wrongly accused and convicted of murdering her baby daughter, and the media made hay of the fact that she didn't act the way they thought was right. She was probably dazed or numb with grief, but to them, the fact that she wasn't bawling her eyes out made her guilty. She was eventually released... but all up, it was not one of the Australian legal system or media's proudest moments.
This accusation was also levelled at the McCann parents about the still-unsolved disappearance of their child Madeleine in Portugal in 2007.
There've been several murder trials where the prosecution has made it a point to mention that the defendant didn't appear upset at the death of the victim, including bringing in several witnesses to testify about it. Checking on the life insurance of the victim, even if you have children whose future is your responsibility, is also brought up if it was done soon after. Apparently, if you are really grieved about someone, you are unable to think about financial matters for at least a few weeks. Just tell the kids that you don't know if they will be soon living in the streets until you check on that next month.