There are so many chemicals to test for, and so many of them have other common uses that using chemical tests as a proxy for malicious intent has poor accuracy. Even assuming tests are extremely accurate, false positive rates would still massively exceed the incidence of threats.

What you look like will greatly increase your odds of being "randomly" searched and thereby odds of false positive chemical detection, at which point what you believe may become a liability during your interrogation.

Having an objective mechanism in the mix doesn't really put a dent how culturally and racially biased the present solution is.

Whether you feel a need for there to be such a system in place only changes whether such a bias is a matter of xenophobic overreach or a technical weakness against threats that resemble the majority.

Yes. Get into their mentality. The lower ranks are underpaid would be burger flippers and In-and-Out. The go through their boring day pushing prodding people. If they get to "interrogate" someone or humiliate him or show off their power just like a bully would in the cafeteria you betcha they'll take advantage of that.

Yeah, Schneier calls it Cover Your Ass Security. It's not super effective ..

https://www.schneier.com/blog/archives/2007/02/cya_security_...

Because people who handle explosives and cover it up when questioned, and aren't involved in handling explosives in their day job, are completely to be trusted?

Surely once they've determined he isn't carrying explosives they need to be sure as possible, if he claims not to have been around any explosives, that he's telling the truth; in order to reduce the risk that he's going to use explosives in an illegal way and/or manner dangerous to life. Don't people who're manufacturing explosives in secret deserve at least a passing glance to see what they're doing with them.

It looks here like they checked his apartment to corroborate his statements.

Now if they've established there are no traces of explosive present - for example they confirm the cause of a false-positive - that's different.

The problem with your line of thought is that you trust that machine to be somewhat reliable. We don't _really_ learn what set off the machine, but the author's guess is an over the counter spray..

If that's the high tech "You need to endure this process for the greater good, since the machine claims you're a threat" world you like to live in, I .. opt out. That thing is obviously next to useless and probably as effective as a look in the eyes of the stranger, with your gut deciding if he's going to stay put for the rest of the day or if he's allowed to move on.

IFF we had a reliable, working test with little to no false positive due to f*ing everyday stuff (or .. bad luck, being a 'random' match), THEN you might have a point. Right now, you don't.

And your problem is you assume the machine isn't reliable. So then if it's set off, you just say "ah well, it's probably a false reading". At that point you just obviated the purpose of the machine.

Yes we don't learn whether it was the permethrin (? can't certainly recall the name) but the people who did the sweep of his apartment confirmed that there were no other indications of explosives manufacture [or you can plump for the slightly less cynical - 'the questioning confirmed he was not a threat'].

There's likely always going to be some false-positives: the needs of the many, yadda, yadda.

>IFF we had a reliable, working test with little to no false positive due to fing everyday stuff* //

Can you post your source and the pertinent stats for the number of false-positives for explosives detection at airports in the USA please.

If you subject a random American to this HIV test and the test result is positive, what is the probability that that person has HIV? I wont do the math, but the right answer is about 2%. Since the prevalence of HIV is so low it doesn't matter how accurate the test it, it will still generate many times more false positives than true ones.

Same thing with bombs. The number of American air passengers/year is about 800 million/year and of them, at most 5 are carrying explosives. Even if the bomb detector is 99.9% accurate it will generate thousands of false positives for each real bomb it catches.

But this doesn't mean that scanning for explosives is a bad idea, or that people should just be merrily flagged to go on their way, otherwise what is the point of doing any screening?

After all, the vast, vast majority of passengers are just trying to go from point A to point B so each and every single scanning method will generate thousands of false positives every year.

YOU started supporting the process and said something like Don't people who're manufacturing explosives in secret..

Well, based on what evidence? The machine that detects chemicals here? It seems that this supports my claim, you think that machine is 'working' and somewhat reliable. Without having provided any kind of proof or source, by the way.

The article, the author, proceeds to talk about potential chemicals to set off the detector (and we had more posts like this over the years, for example from people working with plants, farmers etc). Chemicals you're able to get everywhere.

If that is a known issue and this machine can beep if

a) you've built a bomb

b) you've moved your plants from inside the house to your garden

then you should reevaluate the idea of this particular test in the first place. The author writes that one participant in that theater claimed to know the exact substance that triggered the detector. Really? In that case it should be possible to

- dismiss the idea, it's stupid. That stuff? Everyone can buy it

- ask disguised/hidden questions to reveal if he used one of the gazillion things that might trigger this warning and leave the man alone

The option

- keep him, make him feel like a criminal, treat him in an inhuman (no water..? Really?) way for as long as it takes to break into his appartment

is really not on the list of things you can rationally describe as necessary. That's insane.

Ah, well. I come up empty handed at the end and cannot provide a source for the reliability of the detectors used in the US of A. I guess that makes my whole post moot. Obviously you don't need to provide the same thing, since "It's used at the airports, certainly it works!"?

It's more complicated than that. Anecdotal evidence suggests the trace analysis machine has a very low false positive rate. The fact that agents are trained to re-run the test repeatedly also suggests the machine has a very low false negative rate.

Given a sufficiently low false positive and false negative rate, the right answer may be, if it repeatedly triggers on a passenger, to question that passenger further.

Of course, with increasing reliability of the test comes increasingly severe questioning when the test repeatedly fails. In theory you want the level of the response to be commensurate with the reliability of the test. A perfect test convicts you as soon as you fail it. An imperfect test such as this requires humans to actually follow-up and investigate the failure.

The tactics, ethics, and legality of the how that investigation proceeds... I think that's another matter entirely, from whether we should be employing trace analysis in airports in the first place.

Checked? That's being charitable. You mean it's okay to break into someone's apartment without a warrant and steal shit? What happened to the rule of law? Having said that, we don't know who broke in or what happened.

"This guy set off explosive detectors at the airport. He claimed it was because of chemicals he used while moving. We'd like to check his story out by searching his place." Looks to me like that could convince a judge.

"You’ll have to understand, when a person of your… background walks into here, traveling alone, and sets off our alarms, people start to get a bit nervous. I’m sure you’ve been following what’s been going on in the news recently. You’ve got people from five different branches of government all in here - we don’t do this just for fun."

That's profiling.

Edit to add: in other words "The questions about race/religion weren't profiling, because they weren't used to select him for additional scrutiny" is false. They even admitted to subjecting him to additional security because of his "background".

Simple example: Cop tells Joe Blow that they have a witness to the crime, and Joe Blow may as well confess. Joe Blow makes a full confession. Turns out there was no witness. Perfectly legit; what Joe Blow should have said (if anything) was 'there couldn't be, because I didn't commit that crime.'

Yes, that means that agents of the state (LEOs, prosecutors etc.) have an incentive to misbehave, but in the common law system the adversarial nature of the legal process allows the defense to challenge that. In a civil law system the investigating officer is supposed to be compelled to search for truth above all else, but if the investigating officer is corrupt or inefficient it is much harder to challenge in court, and defense attorneys are much less aggressive on behalf of their clients.

In terms of courts, I'm not sure what context we're talking about, since there are no courts involved. IANAL, but if the OP were to sue, rules about testimonial hearsay don't apply because it would be a civil case, not a criminal one. Even if it were criminal (if the OP had been arrested and was mounting a defense or the FBI agent was, I guess, arrested?), it's not obvious to me that the agent's statement qualifies, since its purpose has to be to assist the investigation. And finally, the rule that police are allowed to lie to get you to confess (as in your example) is actually separate from whether it's testimonial or not, and simply hinges on whether it's coercive. If I understand it, the testimonial hearsay rule as applied to cops lying is for when the cop says, "Oh, it's no problem; I make bombs at home too" in that it doesn't allow the defense to say, "see that cop makes bombs!" So that's all to say I don't understand what all that has to do with whether the OP was being profiled or not. Possibly I misunderstood something or have my legal facts wrong, though; can you clarify?

Edit to add: but regardless, it shouldn't change how much we're outraged at home, assuming we believe the OP's story, which I certainly do.

Who cares if it's legal testimony? It's still racial profiling, which is still uncool for any reason.

No, it's not. He was picked because he set off explosive detectors. Repeatedly.

The racial opinions of the person asking the questions doesn't change the fact that this is not racial profiling.

  nervous = background && companions && alarm

The FBI agent did not say "You are being subjected to additional screening because of your background and because you're traveling alone". That they are nervous because of his background and lack of companions is orthogonal to the fact that the additional screening happened because of the positive match for explosives.

Or are you suggesting that if a white person traveling with companions matched positive for explosives, that they wouldn't be subjected to additional screening?

  1. he sets off the chemical detector
  2. he is pulled aside for questioning
  3. in that questioning, they discover he has a background that makes them nervous
  4. they hold him for a great deal more questioning

The alarms have already gotten us to 2, and they're not even nervous yet, because they don't know his background and, like you said, without the background being true, the whole expression evaluates to false. That's why the 3->4 transition is a problem, and that's where the profiling comes in. The agent's explanation isn't some non-sequitur, like "yeah, this is totally standard and incidentally we're nervous". He's explaining why they're holding him longer and have brought in agents from five different departments instead of just having a TSA guy chat with him and send him on his way. Notice the escalation as they become more concerned; they care about his background because it makes them think he might be a terrorist. Holding people for questioning when they're nervous that the passenger is a terrorist is actually their job. That's why they did so much, even to the point that they felt the need to explain it.

If answers about his background would not change their behavior towards him, why would they ask about it all? The whole point of gathering information is so that you can make decisions with it.

So then we get to the crux of it: his background makes them nervous and their nervousness causes them to subject him to additional scrutiny, above and beyond the screening he would have endured had he set off the alarm and not had a nervousness-causing background. That's profiling.

E.g. if a given test were to generate a false positive, you would expect that it wouldn't generate a false positive the next time if run on the same article, especially if the machine correctly doesn't alert on other innocuous articles.

So in the normal situation someone sets of the chemical detector, once, gets pulled aside for questioning. Their gear doesn't set off the detector again and so the agents are able to conclude it's a false alarm.

To be clear, I don't agree with the treatment OP received in this case, but I fail to see how it is sinister that someone repeatedly sets off chemical detector alarms (that no one else sets off repeatedly), has burned all ties to his residence, is religious and is going up to meet family for a religious gathering.

It's not that such behavior is automatically suspicious, it's that the behavior is still almost indistinguishable from those who previously have caused terrorist attacks.

In this case the FBI agent isn't trying to prove OP a terrorist as much as he's trying hard (and failing) to prove that he's not.

I don't think that's true. Remember that the test doesn't actually detect bombs. It detects certain chemicals. Now, sometimes it might just randomly report a false positive and then you'd expect it not to trigger the second time. But some of the chemicals it is built to detect can be found in everyday products, such as hair products, soaps, some medications, and--as I learned today--bug spray. And so for those chemicals, it's going trigger repeatedly because the chemical it's looking for really is there. So that second failure mode is actually pretty common, and so even when that happens, it's normal to take the person into a side room, search them more throughly, talk to them for a few minutes, and send them on their way. What we see here is quite different.

Which leads us to the real reason, which you wrote:

> It's not that such behavior is automatically suspicious, it's that the behavior is still almost indistinguishable from those who previously have caused terrorist attacks.

That's precisely profiling: "the bad guys have profile x and you fit profile x, so we think you are suspicious" where x isn't inherently suspicious. It sounds like you're saying, "profiling isn't such a bad idea", which I strongly disagree with, but I suppose that's a different discussion.

From what I am hearing from others, normally people barely even get that much special treatment after a non-transient false positive. Agents suggesting "Maybe it was 'Innocuous Product X'" so the passenger can say "Yup, that is probably it" seems to be common, but not the sort of treatment they are going to give to people that they have a bias against.

Well yes, I would. Some false positives can be transient, others are not. If I just came from the shooting range I would not be surprised if I got a non-transient false-positive. Now that is an obvious case and I would immediately tell them that I had been to the shooting range, likely resolving the issue, but it is just a simple example of a false positive that is not transient.

How common is a non-transient false-positive where the victim doesn't immediately have a good idea what the cause is? Well, there are several reports from HN users in this thread that describe situations in which it could allegedly occur. One cites hand lotion as a potential cause of non-transient false-positives; luckily for his wife the agents volunteered that hypothesis so she wasn't left guessing. The author of the article supposes that an over-the-counter chemical was the cause of his non-transient false positive; it's not like he was a lab tech working with synthesized stuff that nobody else ever comes into contact with.

Unless the machines are shit (a distinct possibility), I would expect transient false-positives to be relatively infrequent while non-transient false-positives would be reliably and regularly caused by a wide range of substances that share chemical properties with known explosives.

Most of these non-transient false positives are likely quickly resolved without much ado. His was not.

Edit:

Perhaps the real problem here is with the terminology. These machines are not really bomb detectors, or even explosive detectors. They are chemical detectors. Calling them bomb or explosive detectors is like calling a metal detector a "gun detector". Sure, finding those things may be why it is there, but that is not actually what it does.

Which makes the detectors useless as an interrogation tool.

If the alarm sounds, then check the person for explosives. That makes perfect sense, it's a useful tool for finding explosives on people.

But if you cannot find explosives on the person, what do you do then?

Any even slightly training terrorist is going to know what other products would produce the same detection result as the bomb they just built. So they'll pretend to think for a while, and then say "I work in a supermarket, and a customer dropped hand lotion on the floor this morning, and I had to wipe it up... can that set off your machine?"

It seems like there's a magic answer you can give that will let you go free, you just need to know the right thing to say. If the investigator likes you (i.e. thinks you're probably not a terrorist) they'll give you hints about what you should say. If they don't then you're on your own.

Someone who can give the right answer is either:

* Good at analysis, so they can make a good guess of what might be setting of the machine.

* Someone who's been through this before

* Someone who got a friendly hint from the investigator

* A not-so-dumb terrorist

Someone who can't give the answer is either:

* A normal person

* A dumb terrorist

Given the low prevalence of terrorists, that would be the least likely explanation in either scenario, so the whole line of questioning is pretty much useless, except as a way of applying pressure to someone who you've decided is worth applying pressure to. When that decision is based on some genuine piece of evidence, then it might be a legitimate law enforcement technique. When it's based on the gut-feel of the officers in question, it becomes a front for racial profiling.

The last time I was travelling, I set of the metal detector in an airport in Germany. They took me aside and used the hand metal detector. It also went off. So they patted me down and scanned me again - the alarm still went off. So they patted me down a second time and scanned me again and the alarm still went off.

They then sent me on my way and I had no further hassle for the rest of the trip.

  They even admitted to subjecting him to additional security because
  of his "background".

  1. He sets off the chemical detector
  2. He is pulled aside for "additional security"

  1. He sets off the chemical detector
  2. He is pulled aside for "additional security"
  3. They probe into his background to build a profile
  4. This profile yields further rounds of "additional security"
     that people not matching that profile wouldn't be subject to

> "... because he repeatedly set off the bomb detector."

No, the initial pat-down set off a chemical detector. He set it off once before being pulled into the private room. From that point on, it doesn't matter how many more times it was set off. It shouldn't increase the level of suspicion each time.

Would they have let him go if one time it suddenly stopped giving a positive signal? I doubt it.

> "These sorts of batteries were pioneered by the Israelis and are very effective."

But this is not how the Israelis run their security procedures, so the comparison isn't fair. http://en.wikipedia.org/wiki/Ben_Gurion_Airport#Security_pro...

But this 'It works so well at Ben Gurion' statements get old, really quick. It doesn't.

Traveling to TLV is fine and no problem. Getting out just sucks. I feel treated like shit every single time, it's just borderline acceptable half the time (the other half it's really, really annoying, causing delays and trouble, stupid, braindead, unnecessary, idiotic, etc. etc.).

This coming from a German that lived for one year in TLV and works for a company that sits in IL, so I've been there before my relocation and afterwards. Currently I'm at 14 or 15 visits only, so .. my data points are obviously too few and I just managed to pick the wrong time? Right?

Previous: https://news.ycombinator.com/item?id=5866764

Short version: No, the Israeli version doesn't make you feel like a human being either, most of the time.

Also, I'm not in the slightest bit offended. I'm not Israeli and although my name is Persian in origin (I think?), I'm British. When I travel to the US, I usually get sent to 'secondary', so I've hsd a little experience with this type of questioning. It's just tedious.