SCOTUS suggests in Townsend v. Sain, 372 U.S. 293, that a subject's
confession was constitutionally
inadmissible if it was adduced by police questioning during a period
when petitioner's will was overborne by a drug having the properties
of a "truth serum."
In Miranda v. Arizona, it is held that
If the interrogation continues without the presence of an attorney and
a statement is taken, a heavy burden rests on the government to
demonstrate that the defendant knowingly and intelligently waived his
privilege against self-incrimination and his right to retained or
appointed counsel. Escobedo v. Illinois, 378 U. S. 478, 490, n. 14.
This Court has always set high standards of proof for the waiver of
constitutional rights, Johnson v. Zerbst, 304 U. S. 458 (1938), and we
reassert these standards as applied to in-custody interrogation.
Subsequently in Colorado v. Connelly, defendant suffered from psychosis that "interfered with his ability to make free and rational choices and, although not preventing him from understanding his rights, motivated his confession." The court found that
Coercive police activity is a necessary predicate to finding that a
confession is not "voluntary" within the meaning of the Due Process
Clause. Here, the taking of respondent's statements and their
admission into evidence constituted no violation of that Clause. While
a defendant's mental condition may be a "significant" factor in the
"voluntariness" calculus, this does not justify a conclusion
that his mental condition, by itself and apart from its relation to
official coercion, should ever dispose of the inquiry into
constitutional "voluntariness."
In the Massachusetts case Commonwealth v. Hilton, 443 Mass. 597, the Mass. Supreme Court (in the first ruling) said that
We see no error in the judge's finding that the defendant's mental
infirmities were such that she did not understand the Miranda
warnings, and we therefore conclude that statements made after the
interrogation did become custodial were properly suppressed.
On remand and after in a second appear, in
Commonwealth v. Hilton, 823 N.E.2d 383, the Massachusetts Supreme Court ruled that
a finding that the defendant was unable to make a knowing, voluntary,
and intelligent waiver of her Miranda rights is not enough, standing
alone, to support the finding that her statements were involuntary.
The court found that the defendant was competent to stand trial contrary to the trial judge's determination, and said that
because we are unable to determine if the judge would have allowed the
supplemental motion to suppress without the erroneous findings, we
vacate the order for suppression and remand for further consideration.
The point here is that being mentally disabled is not per se proof that a confession is involuntary.
Turning specifically to intoxication, in Colorado v. Jewell, the trial court suppressed a confession while intoxicated "based on its finding that Jewell was too intoxicated to knowingly and intelligently waive his right to remain silent." The Colorado Supreme Court reversed the suppression
[b]ecause the facts do not support the trial court's determination
that Jewell's intoxication was so severe that he was demonstrably
unable to knowingly and intelligently waive his Miranda rights
which leaves open the possibility that there is some such degree of intoxication. The court determined that
Intoxication only invalidates an otherwise valid Miranda waiver if the
court finds through a preponderance of the evidence that the defendant
was incapable of understanding the nature of his rights and the
ramifications of waiving them.
Subsequent discussion partially fleshes out how one might determine whether a waiver is unknowing or unintelligent. Citing Colorado v. Kaiser, the court suggested considering
whether “the defendant seemed oriented to his or her surroundings and
situation; whether the defendant's answers were responsive and
appeared to be the product of a rational thought process; whether the
defendant was able to appreciate the seriousness of his or her
predicament, including the possibility of being incarcerated; whether
the defendant had the foresight to attempt to deceive the police in
hopes of avoiding prosecution; whether the defendant expressed
remorse for his or her actions; and whether the defendant expressly
stated that he or she understood their rights.”
One issue was raised regarding "cases where, as here, the intoxication is self-induced." A fundamental result of the mass of Miranda case law is that coercive actions by police invalidate a confession. Getting a suspect drunk(er) would be a clear case of a coercive police action, and presumably would be inadmissible under Townsend v. Sain.
