criminal-law us-constitution military investigation
Are the U.S. military police allowed to operate on U.S. soil?
<p>Recently I saw an action movie about military police officer in the U.S. One question surfaced for me - as far as I understand main task of military police (including its investigators) is to combat crime inside U.S. army (and crime related to the army). On the other hand, as far as I remember almost in every country, including U.S., army cannot be used on the domestic territory for pretty much any operations. As I understand, military police is part of the military and technically any investigation or operation which military police will perform would be a violation of this ban on usage of army in homeland.</p>

<p>How this paradox is resolved from legal perspective? Am I misunderstanding something?</p>

<p>It's probably not a good idea to take action movies as authoritative sources on the law. The law that you're referring to is presumably the Posse Comitatus Act (<a href="https://www.law.cornell.edu/uscode/text/18/1385" rel="noreferrer">18 USC 1385</a>) which says</p>

<blockquote>
  <p>Whoever, except in cases and under circumstances expressly authorized
  by the Constitution or Act of Congress, willfully uses any part of the
  Army or the Air Force as a posse comitatus or otherwise to execute the
  laws shall be fined under this title or imprisoned not more than two
  years, or both.</p>
</blockquote>

<p>There is <a href="https://www.loc.gov/rr/frd/Military_Law/Military_Law_Review/pdf-files/175-03-2003.pdf" rel="noreferrer">an article on the act</a> which reviews the pre-history of the act and subsequent congressional authorizations, and there have been many, e.g. the Rivers and Harbors Act of 1894, Espionage Act of 1917, <a href="https://www.law.cornell.edu/uscode/text/33/3" rel="noreferrer">33 USC 3</a> pertaining to gunnery ranges, Fisheries and Conservation Management Act of 1976 and so on. The military police are authorized to enforce military law (though not civilian law), see <a href="http://www.ucmj.us/sub-chapter-2-apprehension-and-restraint/807-article-7-apprehension" rel="noreferrer">article 7 of the UCMJ</a>, authorized by Congress in <a href="https://www.law.cornell.edu/uscode/text/10/subtitle-A/part-II/chapter-47/subchapter-II" rel="noreferrer">Title 10</a>.</p>

<p>P. 167 of the article discusses limits on arrest and investigative powers: their powers pertain almost exclusively to the military.</p>
