In a criminal case, a defendant may introduce evidence of a pertinent character trait. Once the defendant opens the door, the prosecution may rebut with contrary character evidence.

Character evidence is generally inadmissible to prove propensity or conduct in conformity with a character trait. However, it may be admissible for non-propensity purposes or when character is directly at issue.

To prove the contents of a writing, recording, or photograph, the original is generally required. Duplicates are admissible unless authenticity is genuinely disputed or unfairness would result. Oral testimony is permitted if the original is unavailable for reasons other than bad faith.

A jury may compare a disputed signature with an authenticated exemplar to determine authenticity.

A voice may be identified by anyone familiar with it, even if the familiarity was acquired for purposes of litigation or during trial.

Evidence must be authenticated by sufficient proof that the item is what the proponent claims it to be. Authentication may be established through witness testimony, distinctive characteristics, or chain of custody evidence.

A witness must be competent and possess personal knowledge of the matter to testify. Witnesses must also be capable of understanding the duty to testify truthfully.

Withdrawn guilty pleas, pleas of nolo contendere, and related statements are inadmissible under the Federal Rules of Evidence.

Evidence of liability insurance is inadmissible to prove negligence or ability to pay a judgment. Settlement offers and offers to compromise are inadmissible to prove liability or the validity of a claim. Offers to pay medical expenses are inadmissible to prove liability, although accompanying factual statements are admissible under the FRE. Subsequent remedial measures are inadmissible to prove negligence, culpable conduct, product defects, or defective design, but may be admitted to show ownership, control, or feasibility of precautionary measures if disputed.

Relevant evidence may nevertheless be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusing the issues, misleading the jury, undue delay, wasting time, or needlessly presenting cumulative evidence.

Evidence is logically relevant if it has any tendency to make a fact of consequence more or less probable.

A confession may still be considered voluntary even if the defendant suffers from a mental illness. Mental disease or defect alone does not make a confession involuntary under the Fourteenth Amendment.

A confession may still be considered voluntary even if the defendant suffers from a mental illness. Mental disease or defect alone does not make a confession involuntary under the Fourteenth Amendment.

Under the Durham test, a defendant is not criminally responsible if the unlawful conduct was the product of a mental disease or defect.

Under the Irresistible Impulse test, a defendant's mental illness rendered them unable to control their actions or conform their conduct to the requirements of the law.

Under the Model Penal Code test, a defendant suffers from a qualifying mental disease or defect if they are either: (1) unable to appreciate the criminality or wrongfulness of their conduct; or (2) unable to conform their conduct to the requirements of the law.

Under the M'Naghten test, a defendant suffers from a qualifying mental disease or defect if they are either: (1) unable to understand the nature and quality of their acts; or (2) unable to understand that their conduct was morally wrong.

An insanity defense based on a severe mental disease or defect is generally evaluated under one of four tests: (1) the M'Naghten Test; (2) the Model Penal Code Test; (3) the Irresistible Impulse Test; or (4) the Durham Test.

Involuntary manslaughter generally arises in two situations: (1) a killing caused by criminal negligence or recklessness. Criminal negligence requires a gross deviation from the reasonable person standard, greater than that required for civil negligence; and (2) a killing resulting from an unlawful act, including the commission of a misdemeanor or a felony that does not qualify under the felony murder rule.

Voluntary manslaughter is an intentional killing committed in response to adequate provocation. Adequate provocation exists when: (1) the defendant was actually provoked into a sudden heat of passion; (2) a reasonable person would also have been provoked; (3) there was insufficient time for a reasonable person to cool off; and (4) the defendant did not in fact cool off before the killing.