All 3 Uses of

coincidence
in
In Cold Blood

Then, responding to questions, he said no, neither of the women had been "sexually molested," and no, as far as was presently known, nothing had been stolen from the house, and yes, he did think it a "queer coincidence" that Mr. Clutter should have taken out a forty-thousand-dollar life-insurance policy, with double indemnity, within eight hours of his death.†
Chpt 2

coincidence = a situation where things happened at the same time by chance even though it was unlikely

What had they discovered that could not be interpreted as plausible, though exceptional, coincidence?†
Chpt 3 *

The results of the test, to the dismay of Osprey's sheriff as well as Alvin Dewey, who does not believe in exceptional coincidences, were decisively negative.†
Chpt 4

coincidences = situations where things happened at the same time by chance even though they were unlikely

Definitions:

(1) (coincidence)
a situation where two things happened at the same time or in the same way by chance even though it was unlikely

(for example, if two students in the same class met by accident while visiting another country)
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely coincidence can refer to things coinciding (occurring or operating at the same place or time). For example:
- the coincidence of a target and cross hairs
- the coincidence of entangled particles in quantum physics