Document ID: ./input/supremecourt_opinions/opinions/22pdf/21-1496_d18f.pdf
Page Number: 27.0

Cite as:  598 U. S. ____ (2023) 

21 

Opinion of the Court 

be taken as inflexible codes; rather, they should be under-
stood in light of the common law and applied as a frame-
work  designed  to  hold  defendants  liable  when  they  con-
sciously  and  culpably  “participate[d]  in”  a  tortious  act  in
such a way as to help “make it succeed.”  Nye & Nissen, 336 
U. S., at 619 (internal quotation marks omitted).  And the 
text  requires  that  defendants  have  aided  and  abetted  the
act of international terrorism that injured the plaintiffs—
though that requirement does not always demand a strict 
nexus between the alleged assistance and the terrorist act. 

IV 
Under  the  appropriate  framework,  some  aspects  of  to-
day’s  case  become  immediately  clear:  First,  because  they
are  trying  to  hold  defendants  liable  for  the  Reina  attack,
plaintiffs must plausibly allege that defendants aided and 
abetted ISIS12 in carrying out that attack.  Next, plaintiffs 
have satisfied Halberstam’s first two elements by alleging
both  that  ISIS  committed  a  wrong  and  that  defendants
knew  they  were  playing  some  sort  of  role  in  ISIS’  enter-
prise.  The key question, therefore, is whether defendants 
gave such knowing and substantial assistance to ISIS that
they culpably participated in the Reina attack.  The allega-
tions  here  fall  short  of  that  showing  under  Halberstam’s 
framework as properly understood by reference to the com-
mon-law principles it applied. 

A 

To start, recall the basic ways that defendants as a group 
allegedly helped ISIS.  First, ISIS was active on defendants’ 

—————— 

12 For purposes of this case, we need not resolve whether defendants 
must have aided and abetted ISIS, Masharipov, or some subgroup of ISIS 
operatives in committing the Reina attack.  In other words, we need not 
resolve whether “the person” referred to in §2333(d)(2) encompasses in-
ternational terrorist syndicates or is somehow otherwise limited; either 
way, defendants need to have aided and abetted that “person” in carrying 
out the Reina attack.