A foundational text of sociology is Durkheim's Suicide, based precisely on the premise that the act itself is undeniable, that bodies are very hard to hide, and that the motivations, if not an extreme of altruism, are an extreme of either loss of social context (individuation), or complete hopelessness (fatalism).

Suicide has been chosen as its subject, among the various subjects that we have had occasion to study in our teaching career, because few are more accurately to be defined.... Suicide as it exists today is precisely one of the forms through which the collective affection from which we suffer is transmitted; thus it will aid us to understand this.... [I]n common terms, suicide is pre-eminently the desperate act of one who does not care to live.

Moreover, of population suicide rates:

Not only is this rate constant for long periods, but its invariability is even greater than that of leading demographic data.

That is, deviations from norm are intrinsically significant.

https://en.wikipedia.org/wiki/Suicide_(Durkheim_book)

https://archive.org/details/DurkheimEmileSuicideAStudyInSoci...

The problem with a suicide cluster isn't in determining the cause. It's the fact itself.