Is That A Gun In Your Pocket?


By Katherine Lazarow

Detective Herlihy, father of three, surprised his wife with a bracelet on Valentine’s Day and went off to work. A few hours later, he was caught in a deadly shootout in a crowded subway station.

Michael McBride, 52, was wanted for the Monday shooting of his girlfriend’s daughter. According to witnesses, he’d concealed his .22-caliber revolver in a folded copy of the NYDaily News. When street detectives recognized him and called out for him to stop, he raced into the station, where the gun battle ensued.

At least 17 shots were fired at West 145th Street and St. Nicholas Avenue in Harlem, scattering commuters and killing Mr. McBride.

Det. Herlihy was wounded but survived. Many other officers are not so lucky.

“Isn’t there a way of getting handguns out of the hands of potential criminals” ? That’s the question the media and the public ask each time an incident like this occurs.  The NYPD believes it may have the answer.

Welcome to the new world of crime prevention envisioned by Terahertz Imaging Detection, a new technology that measures energy coming off of a person’s body, and detects anything that’s blocking that energy, such as a gun. Currently being tested by the NYPD, it consists of a portable scanner placed on police cars that can be aimed at a particular person to reveal any concealed weapons. Terahertz rays (also called T-rays) are similar to x-rays but less powerful; they can penetrate fabrics and plastic, but can’t pass through metal or water.

The T-ray scanner could be a valuable tool in the battle to reduce the crime rate and prevent gun violence. But at what cost? If the police use the scanners to check every person walking down a particular street for concealed weapons, are they violating these citizens’ right to privacy under the Fourth Amendment? What if the T-ray scanners are used only after a person has been stopped by the police due to suspicious behavior?

The media didn’t carefully examine these questions.  We will.  

The Fourth Amendment protects people against “unreasonable searches and seizures” conducted by the government, and so the first question is whether law enforcement’s use of T-ray scanners amounts to a “search.” If there is no search, the Fourth Amendment doesn’t apply, and the police are free to use the scanners indiscriminately. But if the government’s action is considered a search, then the Fourth Amendment requires that the search be “reasonable.”

In the 1967 case of Katz v. United States, the U.S. Supreme Court stated that, to determine whether certain government conduct rises to the level of a “search” within the meaning of the Fourth Amendment, courts should consider first whether a person has demonstrated a subjective expectation of privacy, and second, whether this expectation is “one that society is prepared to recognize as reasonable.”

Some critics argue that the Katz test hinges on society’s expectations of privacy, and as technology advances and lowers the degree of privacy people expect in their daily lives, the Fourth Amendment will provide less and less protection.

Think of Facebook and Twitter, and the increased use of full body scanners in airports; in the near future might we acquiesce to police using scanners to check for hidden weapons as we walk down the street?

Maybe. But for now, at least, the use of T-ray scanners is probably a “search”: in choosing to put on clothes every day, we expect to keep what’s underneath them private. And this expectation of privacy is almost certainly something that society recognizes as reasonable.

The use of T-ray scanners is also similar to the use of other technology that the Supreme Court has decided is a search. In Kyllo v. United States, 2001, a DEA agent, sitting in his car outside a suspect’s apartment building, used a thermal imaging gadget to measure the level of heat coming from the building, apparently to determine if the suspect was hiding a large marijuana-growing operation. The Supreme Court concluded that the agent’s use of this “sense-enhancing technology” to obtain information that can’t be seen by the naked eye amounts to a search. The Court also stressed that these thermal imaging devices are not in general public use—presumably, if every Tom, Dick, and Harry owned an infrared radar, the suspect would have no reasonable expectation of privacy.

So it appears that if a police officer scans a pedestrian using terahertz technology to determine if he’s carrying a weapon, this act would be considered a search.

Just to play devil’s advocate for a moment:  the use of T-ray scanners is also comparable to police conduct that the Court has determined is not a search:

In 1983, the Supreme Court held in United States v. Place that using trained dogs to sniff a person’s closed bags for illegal drugs is not a “search” within the meaning of the Fourth Amendment. The Court’s rationale behind this “contraband exception” was that, because the dogs reveal only illegal activity and nothing else, people’s privacy is still protected.

Would the use of T-ray scanners fall under the contraband exception? Possibly, if the scanners can expose only illegally concealed handguns. But that’s probably not the case with T-rays. If the scanners can detect handguns, it’s likely they can also detect other objects, such as cell phones and cameras, or something embarrassing but perfectly legal. (Let your imagination wander.) And what about states that allow people to carry guns under their clothes with a concealed carry permit?  If the scanners would reveal any of these items, this exception would not apply.

So we’ve got ourselves a search.  Now we must examine whether this search is considered “reasonable” under the Fourth Amendment. The general rule is that all searches conducted without a warrant are unreasonable. But there are, of course, exceptions—limited circumstances when warrants are not required.

For example, have you ever wondered why the police can pick you out of the crowd and search your bag as you walk through Penn Station? Thank the “special needs doctrine,” which allows for suspicionless, warrantless searches in situations when the government has an increased interest in safety (think airports, international borders, and crowded train stations). The Second U.S. Circuit Court of Appeals explained in 2006 that under this doctrine, random, warrantless searches in New York City subway stations that were intended to detect explosives did not violate the Fourth Amendment. Protecting the subway system from a terrorist attack is a “special need” separate from general law enforcement, and people have the option to refuse the search if they leave the subway.

The use of T-ray scanners in subway stations or airports may fall under the special needs doctrine, as long as people are given the option to be searched or leave the area. But since the government must have a reason for searches apart from general crime control, using the scanners on sidewalk pedestrians is probably not justified. The officers would be using the scanner to detect concealed guns, not threats to national security — and unlike random searches in subways, pedestrians subjected to T-ray scanners do not have the option to walk away before being searched.

“Stop and frisks” present another situation when limited, warrantless searches are still considered reasonable. The Supreme Court first recognized this narrow exception to the warrant requirement in Terry v. Ohio in 1968. The Court held that when an officer reasonably believes that a person is armed and dangerous, the officer may perform a pat down to determine whether the person is carrying any concealed weapons.

The limited use of T-ray scanners to discover guns or other hidden weapons may be justified under Terry. For example, if someone has been stopped by police officers upon their reasonable belief that he is armed and dangerous,  use of the scanner in place of a pat down may be a “reasonable search” consistent with the Fourth Amendment. But if the police scan everyone passing by, even people they have no reason to suspect are armed and dangerous,  these searches would be unreasonable under Terry.

Terahertz Imaging Detection is not the first technology to scan groups of people to identify potential criminal activity. Face-recognizing cameras that can search crowds and use algorithms to identify faces of known criminals were used at the 2001 Super Bowl in Tampa Bay, and are currently scanning faces in Las Vegas casinos and the New York DMV. License plate recognition cameras, which attach to police cruisers and scan all passing license plates to identify stolen vehicles, are regularly employed by law enforcement without much resistance from the public, too.

And soon, sniffing technology may be installed in airports to detect biological and chemical security threats. The technology samples the air around travelers and identifies whether they have recently been in contact with specific substances, such as explosives.

All this technology has the potential to prevent crimes and save many lives. If the T-ray scanners were available to Det. Herlihy and his fellow officers, it’s possible they would have detected Mr. McBride’s hidden gun and taken precautionary measures to avoid the fatal shootout. On the other hand, unrestricted use of the scanners could also result in the invasion of many innocent citizens’ privacy.

Is this a price we’re willing to pay?

I suspect the widows of police officers killed in the line of duty would say, “yes.”  What about the rest of us?


1 Comment »

One Response

  1. Copier says:


    It appears that you lifted large parts of this article from another blog post, word for word, particularly as it relates to the legal analysis. Please credit it where you got it from.

    Thank you.

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