Thanks for the detailed response.

This answer does a great job of pointing out the minor frame challenge that it's very likely that no one will need to be called; some parties (e.g. from NORAD) might just start showing up. Large space objects really should be noticed before impact.

In addition to the CDC, potentially the Department of Energy and the EPA. The CDCs expertise is primarily biological hazards, if someone is presented with an unknown thing and are worried about it being a hazard, they are going to call people representing the trio of NBC.

@user1937198 Good catch! Added the EPA. What would be DoE's concern?

Jurisdiction, Shmurisdiction - its a race and as with artefacts comes power and power-shifts, reasons, stories and jurisdiction can be created. Just declare it a defector message smuggled out via rocket from north korea, voila..

@Pica That is not how it works. That is not how any of this works. While you, as an average citizen, could not care less about the constitution or the charters of administrative authorities, they do care. They care a whole f...ing lot. The oath they swear to protect and uphold the constitution is not just ceremony nr empty words, it has a meaning that is the foundation of their service. If you claim that they throw the constitution and their charter out the window first chance they get, you are pretty much insulting and denying the integrity of every person that serves the country.

@Pica Also, it is lazy writing, fit perhaps for sunday morning cartoons with an audience of pre-school children that do not know any better. But for anyone with the least bit of understanding about how government and administration of the country works (i.e. not getting an F in Social Sciences) it will be offputting and annoying.

@MichaelK Nuclear material. Any radioactive material or radioactive hazard. They have people who know dose management, decontamination, hazard identification etc.

In the classic NBC trio of hazards, Nuclear is DoE, Biological is CDC, and C is EPA (who also cover the impact of chemical releases into the environment on humans)

@user1937198 Oh! But of course, total brain fart on my part forgetting about that.

I think the military would be more involved. For a long while the UFO will be assumed to be a secret drone sent by China or Russia. And for a long while the biggest question of the intelligence services would be "how could they have developed this thing without us knowing abut it?"

I like the answer, but think CIA will become involved a lot earlier since the assumption that the UFO is actually some foreign spyware or military prototype will likely happen a lot earlier than the realisation that it is actual extraterrestrial intelligence.

@vsz "For a long while the UFO will be assumed to be a secret drone sent by China or Russia" First, that is a far-reaching assumption, and a pretty narrow one. And second, it is still an issue for Homeland Security, not the military.

@fgysin I can imagine a very awkward conversation, condensed here: "CIA, WTF?!" "What?! What did we do?" "Foreign spy drone, on our soil, and you missed it!" "And you know it is foreign, and a spy drone, because...?" "Uhm... well, it has do be." "Mm hmmm... "Wha'?" "You have to do a lot better than that. How do you know it is a foreign spy drone?" "Well, what else could it be?!" "Your lack of imagination — not to mention appalingly poor due dilligence where you have not even looked at the damned thing — is not our problem, and we sure as death and taxes won't take any shit for it. Bye now."

@MichaelK That is one possible interpretation. Another might be: CIA1: "WTF was that? Does is fall within our jurisdiction?" CIA2: "No idea sir." CIA1: "Are you shitting me? How have we missed this?" CIA2: "We have no idea and no clear information about the situation." CIA1: "Well, then get our people out there to find out WTF is going on! Better be save than sorry!"

@fgysin Again, and I have to stress this: jurisdiction. The CIA are not allowed to mount operations on US soil! They are the foreign intelligence service. So they are forbidden from running around doing sketchy [stuff] on their own inside the US. If any intelligence agency wants to get involved in this, it would be the National Security Agency. And in any case, it is not very likely that any of these have any clue what is going on before NTSB has kicked it up to the president, which then will call in the Director of National Intelligence and they will then assign an agency to work on this.

@MichaelK : if a flying object crashes on US soil and it does not look similar to anything made in the US, then the default assumption will be that it is a foreign spy drone. That's the simplest and most obvious first assumption. Immediately categorizing it as extraterrestrial intelligence is what's far-reaching and narrow.

@vsz "the default assumption will be that it is a foreign spy drone" Will it now. Accrding to who or what? Let me remind you that funky looking objects falling from space is not a rare or even surprising occurrence. Some of the most famous cases are Cosmos 954 and Cosmos 1402, which brought serious concerns because of their nuclear reactors, only about 1% of 954s radioactive load was found. A more humorous case was when the Shire of Esperance in Australia fined NASA 400 Australian Dollars for littering when parts of Skylab fell in their territory (written off, but then paid 30 years later).

@vsz So, the assumption — in case something is unknown — that it is a spy drone, is not only hasty, it can even put people at severe risk! "Boss said it is just a spy drone... oopsie, turns out it is highly active nuclear waste... FML... what little is left of it". So, no, I am not buying into your assertion that people will jump to such conclusions / assumptions, it makes no sense at all. If you want claim this is the assumption they will make, I am going to ask you to back it up with something.

@NathanielRobinson I have edited the answer some to clarify how the case moves upwards.

@MichaelK thanks for the edit. I'll make sure to take a look