When it relates to cause of death;

(1) When the statement is made by person as to the cause of his death, or as to any of the circumstances of the transaction which resulted in his death, in cases in which the cause of that person's death comes into question.

Such statements are relevant whether the person who made them was or was not, at the time when they were made, under expectation of death, and whatever may be the nature of the proceeding in which the cause of his death comes into question.