Is an involuntary statement/evidence admissible in court?
It depends on what exactly the evidence is and what makes it involuntary. The court (judge) decides whether or not evidence is admissible. The attorneys argue about it and the judge listens. What the court will look at is (1) the type of evidence (some evidence is admissible even if involuntary or unintentionally provided) and (2) how the evidence was obtained. Other factors may include whether or not the evidence is relevant to the case, unnecessarily inflammatory to a jury, etc.