This section is from the book "Popular Law Library Vol10 Criminal Law, Criminal Procedure, Wills, Administration", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
As a general rule declarations of the deceased relating to the cause and circumstances of his death and by whom he was assaulted are incompetent, being hearsay. But to this rule there is a very important exception.88
Such declarations are competent evidence when made by the deceased under a sincere and settled belief of impending dissolution and moral conviction that immediate death is inevitable, without the slightest hope of recovery. In other words such declarations are made in extremity when the declarant is at the point of death and when every hope of recovery is gone - when every motive to falsehood is silenced and the mind is induced by the most powerful considerations to speak the truth.89
Declarations made under such circumstances are regarded as equivalent to the sanction of an oath. They are substitutes for testimony given in open court under oath,90 and they are competent for the defendant as well as for the prosecution.91
The admission in evidence of dying declarations, when competent, is not a violation of the constitutional provision, "that the accused shall be confronted by the witnesses against him."92
87 State vs. Scott, 49 La., 253;
Hughes Cr. Law, Sec. 2433. 88 Digby vs. People, 113 111., 125;
Com. vs. Casey, 11 Cush.
(Mass.), 421; State vs. Reed, 137 Mo., 125; State vs. Pearce, 56 Minn., 226. 89 Westbrook vs. People, 126 111., 89; People vs. Olmstead, 30
Mich., 431; Simmon vs. People, 150 111, 73.
90 People vs. Olmstead, 30 Mich., 431. 91 Underhill Cr. Ev., Sec. 110;
Skill vs. State, 88 Ala., 14;
Brown vs. Com., 73 Pa. St., 327 92 Brown vs. Com., 73 Pa. St., 321;
State vs. Nash, 7 Iowa, 347;
Hughes Cr. Law, Sec. 90.
Declarations of the deceased must be restricted to the act of killing and the circumstances immediately-attending the act and forming part of the res gestae,93 including the name of the person by whom the deceased was assaulted;94 for, statements of the deceased which are not part of the res gestae are mere hearsay.95
 
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