What is the liability if those falling into a well die due to factors inherent to the well rather than falling upon one another?

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If their deaths result from factors other than falling on each other, such as the depth of the well causing death upon impact, water causing drowning, or a lion causing death, then no party bears financial responsibility for another, due to the lack of causal effect of one's action on another's demise. If there is doubt regarding the cause, no one is held liable, as the default principle is the absolution of responsibility, which is not overturned by mere doubt.