Of course, at this point, there's been no finding that Bostian did anything wrong, let alone anything criminal. Still, these early reports of memory loss open a dialogue about a rarely-invoked defense in criminal law: amnesia. If a defendant is charged with a crime, and doesn't remember the "night in question," can that be a defense to a crime?
Amnesia as a defense to a crime does not come up often, but when it does, it takes two forms: 1) incompetence to stand trial; and 2) amnesia-as-insanity.
Incompetence and insanity are two very different legal concepts. Insanity is an excuse to a crime, whereas incompetence has to do, instead, with your ability to go to trial.
In Pennsylvania, if a defendant is "substantially unable" to understand the nature or object of the proceedings against him, or to participate and assist in his defense, he is incompetent
to be tried, convicted or sentenced, but only so long as that incapacity continues.
Pennsylvania courts have actually discussed whether amnesia is a form of incompetence.
The short answer is: most of the time it's not. To invoke amnesia as incompetence, there must be evidence of an actual mental disability interfering with the defendant's rational understanding. As one court observed, "[M]ere vacuity of memory is not tantamount to legal incompetency to stand trial." So then, amnesia is only incompetence if the memory loss is part of a mental disorder which impairs the defendant's ability to comprehend his position or cooperate with counsel.
Incompetence has nothing at all to do with a defendant's criminal culpability. It has nothing to do with whether he did what he's charged with doing, or whether his actions were excusable. Incompetence really only arises long after the alleged crimes, during the criminal proceedings against the defendant.
Insanity, on the other hand, is all about what was in the defendant's mind at the moment he committed the alleged crimes. Insanity is always a risky proposition, because a defendant essentially concedes he did it, but that he has an excuse for doing it. Unfortunately, in Pennsylvania, the amnesia-as-insanity defense has not fared well.
Courts generally hold that amnesia is not a defense
to a crime, unless the accused, at the time of the act, did not know the nature or wrongfulness of the act. A defendant's inability to remember the "night in question" is not, by itself, proof of a mental condition, either. In some jurisdictions, courts have squarely held that amnesia is not
a "mental disease or defect" under laws excusing criminal conduct by reason of a mental disease or defect. Pennsylvania courts appear to follow the general rule: amnesia is not a defense
to a crime.
Although amnesia is rarely raised, it presents tricky legal issues. For the most part, the public responds to a defense of "I don't remember" with an eye roll and a "yeah whatever." That's because it's convenient for defendants to not remember in certain cases.
For that reason, alleging amnesia will always be an uphill battle, unless a defendant can come up with some high-powered experts to demonstrate that the amnesia was part of a larger mental problem that could qualify for insanity or incompetence on its own. The unexplained temporary memory loss, without a mental condition, will likely remain an unavailable defense for most defendants.