In mystery fiction (not necessarily crime fiction), the important evidence is found by important characters. It doesn't matter how many people are searching, how inexperienced the main character is at mystery solving, or if they are operating out of their field.
They could be off the case, sent home sick, having a day off, late for work, etc. Someone will throw the evidence out the window of a moving car for it to hit them in the face. No matter what, main characters find the evidence.
This trope is understandably found everywhere in mystery fiction, since main characters are meant to drive the plot, yet most authors do not attempt to explain the continuing good fortune of sleuths, both amateur and professional, finding that one piece of evidence that not only seals the mystery up in a neat little package, but also managed to elude everyone else.
Of course, maybe they wouldn't be main characters if this sort of thing didn't happen to them.
A sub-trope of The Main Characters Do Everything
. Related to Busman's Holiday
Anime and Manga
- In Detective Conan, minor characters will only find evidence if it's there to throw them off track.
- In Monk and Psych this is justified — they're the only people in their departments who can find the evidence.
- Ace Attorney, owing to the shocking incompetence of the police force.
- It's also significantly averted,since the cops do find a lot of evidence for the prosecution. Phoenix (or Apollo) is the only one actually looking for evidence that can be used by the defense.
- Danganronpa, mostly due to Kirigiri's talent. Other people find evidence, but do not realize that it may be used as evidence until Naegi or Kirigiri learn of it.
- KateModern, probably because the police are being manipulated by the Order.
- Played with in an episode of Justice League. Batman doesn't find any evidence at a crime scene, and suggests minor character The Atom come to find anything he might've missed. However, he apparently doesn't find anything either.