An accused’s own words to a police officer often represent a valuable source of evidence for the prosecution at a criminal trial.
That being said, an accused’s pre-trial statements to a person in authority are presumptively inadmissible. Pursuant to the common law confessions rule, the prosecution must first persuade the trial judge that the accused voluntarily made the statements beyond a reasonable doubt (see R. v. Oickle,  2 S.C.R. 3).
The word ‘voluntary’ has a special meaning in this context and may best be understood as “shorthand for a complex of values”(Oickle at para. 70).
The voluntariness test involves a consideration of several factors, including whether the statement was obtained as a result of: 1) threats or promises; 2) oppressive circumstances; 3) the lack of an operating mind; and/or 4) police trickery that was so appalling as to shock the community.
A trial judge must “be alert to the entire circumstances surrounding” the making of the statement (Oickle at para. 68).
A trial judge must also be “sensitive to the particularities of the individual suspect” (Oickle at para. 42).
The confessions rule is grounded in concerns about:
1) State conduct that may induce unreliable statements (Oickle at para. 68);
2) The “protection of the accused’s rights and fairness in the criminal process” (Oickle at para. 69); and
3) The maintenance “of the integrity of the justice system” (Oickle at para. 65).
The confessions rule does not apply if the accused made the statement to someone other than a person in authority. An accused's statements to someone other than a person in authority are presumptively admissible.