The agents did several things that escalated the whole deal, things which a cadet would have immediately understood. To quote just a few:

> These events include Mr. Mukerjee becoming further agitated and aggressive after testing positive for explosives, as well as him repeatedly reaching for his not-yet-manually-searched bag.

> However,multiple statements by TSA personnel reference Mr. Mukerjee repeatedly grabbing for his bag after he was told not to touch it.

This is wrong on the following levels:

1. The first fucking thing you do when you detain someone is explain them why they are detained, how long they will be detained and -- if they have not actually broken any law and are there for preventive action, what you are doing in order to prevent it. If you exceed this period by the most infinitely small amount of time, you immediately tell them why it is taking longer (in some civilized countries not doing this is reason enough for the state to start selling politicians' kidneys to pay damages). Basically, what the dudes should have done was say: "Hello Mr. Mukerjee, we have to detain you on the basis of <whatever law they are doing it on> because we have suspicions that you might try to harm the passengers on board. We need to check a few things up, this will take <how much fucking time can it take to check a stupid suitcase and a handbag>. I understand this may sound outrageous to you, but we need to make sure." It's particularly important that you use normal-sounding words and sentences in an active voice. Someone who isn't a regular jail offender will most likely be panicked enough to to understand a word you're saying if you start throwing shit like "we believe you might be a threat to the safety of the crew and the passengers of the vessel".

2. If you don't want people to get agitated, you don't offer them external triggers. If you want to conduct a search, you immediately remove all the bags after conducting a thorough inventory of it in the presence of the guy you're searching. "Mr. Murkjee, we need to search your bag <on the basis of whatever law allows us to do that without a warrant>. Can you please tell me what's inside? We will have to remove all items in another room, we need to make a list of the items inside to make sure you get them all back". Of course people are going to get nervous if they are in danger of losing their work. They kind of depend on it to eat. If you don't remove these belongings, people will naturally keep peeking at them and grabbing them and insisting on touching them because they're afraid. It's a natural reaction.

3. If you detain someone for longer than half an hour, you provide for their needs period. You ask if they need water or a snack. If they're guilty, they'll have a long time to be thirsty and hungry in prison, but there's a long way before that. You do this for two reasons that you hear about in the first six hours of training (if your instructor is slow, it can probably take as little as four...). First, basic sensations of thirst and hunger amplify the sensation of fear. Second, dehydration and low blood sugar levels heighten the symptoms of fear and panic, like anxiety and shaking.

4. When someone tested positive for something, you either don't tell him and get on with it on your own, or you tell him and ask for an explanation. Maybe the dude visited a friend whose kid got a chemistry kit as a present and splashed it all over the table in the living room. Either tell him "Mr. Murkjee, you tested positive for di-hidrogen oxide, a substance we believe may be explosive. We need to conduct a further search through your items -- we have people working on that right away so that you can be back on your trip as soon as possible, but in the meantime, do you know of any way in which you could have come into contact with this substance?". Either do that, or just tell him that their preliminary tests showed traces of an explosive substance, we need to search your items to know for sure if it can be dangerous. In both cases, tell the dude how long it takes. People can have a panic attack just because of missing a flight, can you imagine how awesome it has to be to have someone who carries a gun drag things along when you have a plane to catch?

Bonus things the TSA folks fucked up:

5. If someone wishes to go but you haven't finished your procedure, you fucking tell them why and explicitly mention what you need to do before clearing them. People who fly have no way of knowing, and particularly no reason of knowing the whole procedure. Telling him he can go, but the bag stays was a major fuck-up that is usually reason enough for disciplinary action in a normal police force. You don't just tell people they can go without their items. The correct thing to do is say something along the lines of "Before clearing you for leaving, we need to check your bag, in case it may contain items that could be harmful for the passengers in the terminal. This will take <X minutes>, once we're done you're free to leave if you wish".

6. There is no such thing as a "limbo", not in any sane security procedure. Someone is always in one of three possible states, and if he goes from one to another you immediately mention it: he's either detained (for a definite or indefinite period of time), free to go after a procedure is finished (all suspicions are off, but there's some compulsory stuff that needs to be done -- e.g. you're sent home from the station, but you still need to get the receipt that confirms you received all your items from storage before they clear you to leave) or you're free to go. "There is nothing wrong with you but you can't leave" is a form of abuse period. It does not matter if things aren't that way: what the man sees is what you're telling him. There's no way a boarding passenger knows the whole procedure, so that he can go like "Oh, there's no need for me to worry... I'm ok but they can't let me leave while my bag hasn't been searched. I can't just go and mingle with the people who have been cleared to fly while I haven't, since I might stealthily hand them a knife or a pack of explosives after they've gone through the security check."

7. If the reason you are detaining someone is a subjective one (i.e. the dubious-guy-spotter said he looks dubious), you still need to provide a reason for detaining him. If you don't, the dude will naturally think you just picked him at random, which he will -- again -- perceive as a form of abuse.

tl;dr There are some basic things you need to in order to tell if the person you're talking to is being aggressive or giving inconsistent answers because he's preparing to carry out a criminal offense. If you don't do them, you fuck up your screening process.

Being under pressure is not an excuse for not doing a job you're supposed to do under pressure.

Full disclosure/source: I wanted to spend an year in a computer security-related position for a state institution in my country of origin, and had to take a course on this. My memory of the details is fairly dim, I hope I haven't trashed anything significant.

So maybe it's finding something true. BFD. You look in the bag, verify there's no explosive there, and let him through.

Maybe the bag had fireworks in or near it at some point. Or magician's supplies. Or a chemistry set. Or any number of other things. There are a dozens reasons why a bag might actually have been near explosives or chemicals that are similar enough to explosives or explosive precursors that the test would correctly show positive.

Nobody cares whether the test result was an error or a "correct" reading based on something that IS NO LONGER IN THE BAG - either way, you let him through. Why the hell not?