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4 aliens who are not detained continue to engage in crime and fail to appear for their removal hearings in large numbers.” Demore v. Kim, 538 U. S. 510, 513 (2003). To address this problem, Congress mandated that aliens who were thought to pose a heightened risk be arrested and detained without a chance to apply for release on bond or parole.

Section 1226(c) consists of two paragraphs, one on the decision to take an alien into “[c]ustody” and another on the alien’s subsequent “[r]elease.” The first paragraph (on custody) sets out four categories of covered aliens, namely, those who are inadmissible or deportable on specified grounds. It then provides that the Secretary must take any alien falling into one of these categories “into custody” “when the alien is released” from criminal custody.

The second paragraph (on release from immigration custody) states that “an alien described in paragraph (1)” may be released “only if [the Secretary] decides” that release is “necessary to provide protection” for witnesses or others cooperating with a criminal investigation, or their relatives or associates. That exception is not implicated in the present cases.

The categories of predicates for mandatory detention identified in subparagraphs (A)–(D) generally involve the commission of crimes. As will become relevant to our analysis, however, some who satisfy subparagraph (D)–e. g., close relatives of terrorists and those who are thought likely to engage in terrorist activity, see 8 U. S. C. §1182(a)(3)(B)(i)(IX)–may never have been charged with any crime in this country. Still, since the vast majority of