In March, the Supreme Court unanimously reversed a Massachusetts high court decision that upheld the state’s stun gun ban. The Massachusetts court’s justifications for upholding the ban, the Supreme Court said, were inadequate:

The [Massachusetts] court offered three explanations to support its holding that the Second Amendment does not extend to stun guns. First, the court explained that stun guns are not protected because they “were not in common use at the time of the Second Amendment’s enactment.” This is inconsistent with D.C. v. Heller’s clear statement that the Second Amendment “extends … to … arms … that were not in existence at the time of the founding.”
The court next asked whether stun guns are “dangerous per se at common law and unusual,” in an attempt to apply one “important limitation on the right to keep and carry arms,” Heller; see ibid. (referring to “the historical tradition of prohibiting the carrying of ‘dangerous and unusual weapons’”). In so doing, the court concluded that stun guns are “unusual” because they are “a thoroughly modern invention.” By equating “unusual” with “in common use at the time of the Second Amendment’s enactment,” the court’s second explanation is the same as the first; it is inconsistent with Heller for the same reason.
Finally, the court used “a contemporary lens” and found “nothing in the record to suggest that [stun guns] are readily adaptable to use in the military.” But Heller rejected the proposition “that only those weapons useful in warfare are protected.”
For these three reasons, the explanation the Massachusetts court offered for upholding the law contradicts this Court’s precedent. Consequently, … the judgment of the Supreme Judicial Court of Massachusetts is vacated, and the case is remanded for further proceedings not inconsistent with this opinion.

The Supreme Court, however, didn’t hold that the stun gun ban was unconstitutional — it simply rejected the arguments that the Massachusetts court had given for upholding the ban. The case, which involved the prosecution of a woman named Jaime Caetano, was left to go forward. The state could, for instance, argue that the statute might still pass “intermediate scrutiny” or “strict scrutiny” because it was sufficiently related to a sufficiently important government interest, and the Massachusetts courts would consider those arguments.

But yesterday, Caetano was formally exonerated, by agreement of the prosecution and the defense, so the case is now over; the statute remains on the books, though with a cloud over it as a result of the Supreme Court’s decision. (Indeed, a Michigan stun gun ban had been struck down in People v. Yanna (Mich. Ct. App. 2012), and a Connecticut ban on, among other things, police batons was struck down in State v. DeCiccio (Conn. 2014), an opinion that cited Yanna favorably.)

Indeed, Caetano’s lawyer, Benjamin Keehn, reports that Caetano got more than just dismissal of the charges: Rather, she was formally found not guilty:

The judge … agreed that the record should show that she was vindicated, and found [her] not guilty after a jury-waived, facts-stipulated trial. [The j]udge then allowed a petition to seal her record.
It was all about her record — a record check by a landlord or prospective employer showing that a felony weapons charge had been dismissed (after a guilty verdict had been vacated) would have been very problematic. So the [not guilty] plus the allowed petition to seal should put her as close to what should have been the correct status quo ante, which is that she would not have been charged in the first place for exercising her right to armed self-defense in the face of an unconstitutional statute (which is still on the books — but the client comes first).

Finally, here is a brief description of the facts, from Justice Samuel A. Alito Jr.’s concurrence (joined by Justice Clarence Thomas) in the Supreme Court decision, together with part of Justice Alito’s argument that the statute should have been struck down outright:

After a “bad altercation” with an abusive boyfriend put her in the hospital, Jaime Caetano found herself homeless and “in fear for [her] life.” She obtained multiple restraining orders against her abuser, but they proved futile. So when a friend offered her a stun gun “for self-defense against [her] former boy friend,” Caetano accepted the weapon.
It is a good thing she did. One night after leaving work, Caetano found her ex-boyfriend “waiting for [her] outside.” He “started screaming” that she was “not gonna [expletive deleted] work at this place” any more because she “should be home with the kids” they had together. Caetano’s abuser towered over her by nearly a foot and outweighed her by close to 100 pounds. But she didn’t need physical strength to protect herself. She stood her ground, displayed the stun gun, and announced: “I’m not gonna take this anymore…. I don’t wanna have to [use the stun gun on] you, but if you don’t leave me alone, I’m gonna have to.” The gambit worked. The ex-boyfriend “got scared and he left [her] alone.”
It is settled that the Second Amendment protects an individual right to keep and bear arms that applies against both the Federal Government and the States. That right vindicates the “basic right” of “individual self-defense.” Caetano’s encounter with her violent ex-boyfriend illustrates the connection between those fundamental rights: By arming herself, Caetano was able to protect against a physical threat that restraining orders had proved useless to prevent. And, commendably, she did so by using a weapon that posed little, if any, danger of permanently harming either herself or the father of her children….
The Supreme Judicial Court suggested that Caetano could have simply gotten a firearm to defend herself. But … a weapon is an effective means of self-defense only if one is prepared to use it, and it is presumptuous to tell Caetano she should have been ready to shoot the father of her two young children if she wanted to protect herself. Courts should not be in the business of demanding that citizens use more force for self-defense than they are comfortable wielding.
Countless people may have reservations about using deadly force, whether for moral, religious, or emotional reasons — or simply out of fear of killing the wrong person. I am not prepared to say that a State may force an individual to choose between exercising that right and following her conscience, at least where both can be accommodated by a weapon already in widespread use across the Nation….
A State’s most basic responsibility is to keep its people safe. The Commonwealth of Massachusetts was either unable or unwilling to do what was necessary to protect Jaime Caetano, so she was forced to protect herself. To make matters worse, the Commonwealth chose to deploy its prosecutorial resources to prosecute and convict her of a criminal offense for arming herself with a nonlethal weapon that may well have saved her life. The Supreme Judicial Court then affirmed her conviction on the flimsiest of grounds….
If the fundamental right of self-defense does not protect Caetano, then the safety of all Americans is left to the mercy of state authorities who may be more concerned about disarming the people than about keeping them safe.