Charlotte, North Carolina, SWAT officer Fred Thornton was killed last month when a flashbang grenade exploded as he was securing his equipment in the trunk of his patrol car. This comes a few years after the federal government began a criminal investigation of a firm that manufactured faulty flashbangs, one of which prematurely detonated in 2008, causing permanent injury to three FBI agents.

I explain this in more detail in a column I wrote last year, but the thing to keep in mind is that the only malfunction with the flashbangs in these stories was the timing of their detonation. Had they not gone off prematurely, they would eventually have been used against U.S. citizens, just as they're used every day in America. Most of the time, they're used against people merely suspected of a crime, and most of the time those crimes are nonviolent, consensual drug crimes. That is, by design, when they're used exactly as intended, flashbangs cause serious, sometimes permanent injury to people who have yet to even be charged—much less convicted—of nonviolent, consensual crimes.

The people on the receiving end of a flashbang grenade are undoubtedly just as unprepared for their effects as Officer Thornton or the FBI agents injured in 2004. The grenades and the raids in which they're used are intended to take their subjects by surprise. The grenade's specific purpose is to give officers a tactical advantage in situations where they're entering a house or a room and have no way of knowing what's going on inside. Which means they're deployed blindly. Which means there's a good chance the people subjected to flashbangs—which would include both suspects and innocent bystanders—are in just as defenseless a position as Thornton or the injured FBI agents were.

According to the family of Aiyana Jones, the nine-year-old Detroit girl killed in a police raid last year, the flashbang police tossed through her family's window landed on her blanket, setting it and her on fire just before an officer mistakenly shot her. Flashbangs have set homes on fire (some resulting in fatalities), caused severe burns, and confused police officers into thinking they were coming under gunfire, causing officers to open fire themselves. The blinding, deafening effects have also induced fatal heart attacks. For all of these reasons, the NYPD, to its credit, has stopped using them.

In an interview for my column last year, Clay Conrad, a Texas criminal defense attorney who has challenged the use of flashbangs in court, offered an interesting proposition. "We were prepared to argue that if these things are as harmless as the state claims, we should be able to detonate one in the courtroom. That would have been fun."

I doubt any court would allow that. Which is precisely the point. Weapons like tear gas or Tasers also cause injury, but they're only used (or at least they're only supposed to be used) against someone who has demonstrated that they are an immediate threat to police or those around them. Flashbangs are usually deployed before the suspect has been given a chance to comply peacefully.

The devices that killed Officer Thornton and injured those FBI agents did exactly what they're supposed to do. It's just that from the officers' perspective, the devices went off at the wrong time. We should be asking why we permit the government to routinely use the same devices against U.S. citizens.