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Page Number: 14.0

8 

TWITTER, INC. v. TAAMNEH 

Opinion of the Court 

§2333(d)(2).  The central question is thus whether defend-
ants’ conduct constitutes “aid[ing] and abett[ing], by know-
ingly providing substantial assistance,” such that they can 
be held liable for the Reina nightclub attack.  Ibid. 

III 
As always, we start with the text of §2333.  See Barten-
werfer v. Buckley, 598 U. S. 69, 74 (2023).  Here, that text 
immediately begs two questions: First, what exactly does it
mean to “aid and abet”?  Second, what precisely must the
defendant have “aided and abetted”? 

A 
We  turn  first  to  the  meaning  of  the  phrase  “aids  and 
abets,  by  knowingly  providing  substantial  assistance.”
Nothing in the statute defines any of those critical terms. 
Yet terms like “aids and abets” are familiar to the common 
law, which has long held aiders-and-abettors secondarily li-
able for the wrongful acts of others.  See Central Bank of 
Denver, N. A. v. First Interstate Bank of Denver, N. A., 511 
U. S.  164,  181  (1994).  We  generally  presume  that  such
common-law terms “brin[g] the old soil” with them.  Sekhar 
v. United States, 570 U. S. 729, 733 (2013) (internal quota-
tion  marks  omitted).  In  enacting  JASTA,  Congress  pro-
vided  additional  context  by  pointing  to  Halberstam  v. 
Welch,  705  F. 2d  472  (CADC  1983),  as  “provid[ing]  the 
proper legal framework” for “civil aiding and abetting and 
conspiracy  liability.”    §2(a)(5),  130  Stat.  852.6   We  thus 
begin with Halberstam’s “legal framework,” viewed in con-
text of the common-law tradition from which it arose. 

—————— 

6 The provision reads in full: “The decision of the United States Court 
of Appeals for the District of Columbia in Halberstam v. Welch, 705 F.2d 
472  (D.C.  Cir.  1983),  which  has  been  widely  recognized  as  the  leading
case regarding Federal civil aiding and abetting and conspiracy liability,
including by the Supreme Court of the United States, provides the proper
legal framework for how such liability should function in the context of 
chapter 113B of title 18, United States Code.”  §2(a)(5), 130 Stat. 852.