By Katherine Tomaszewski

Case Summary

On May 18, 2023, the Supreme Court of the United States (SCOTUS) decided Twitter v. Taamneh, holding that Twitter is not liable for aiding and abetting under the Anti-Terrorism Act (ATA) for a shooting attack at the Reina nightclub in Istanbul for which the self-styled Islamic State (ISIS) claimed responsibility.

SCOTUS ruled that Twitter was not liable for aiding and abetting the Reina attack because it did not “knowingly” provide “substantial assistance” to ISIS under the ATA (18 U.S.C. § 2333). SCOTUS’ opinion narrows the scope of liability under the ATA. In doing so, it offers some assurances to non-governmental organizations (NGOs) providing humanitarian assistance or peacebuilding processes in areas where terrorist groups operate, who are concerned about defending against any allegations that their services would inadvertently support terrorist acts.

Following the Istanbul shooting on Jan. 1, 2017, the plaintiffs in this case, relatives of the victims of the shooting, sued Twitter, Google, and Facebook (now known as Meta Platforms, Inc.) under the ATA. The plaintiffs claimed that these companies aided and abetted ISIS by allegedly allowing ISIS members to use its platform to recruit and gain support for ISIS in general. Additionally, the plaintiffs alleged that these companies did not act aggressively enough to take down ISIS content. Notably, there were no allegations or indications in the complaint that ISIS used Twitter or these other platforms to specifically recruit or plan the Reina nightclub attack.

The social media companies moved to dismiss the case, which the District Court granted in October 2018. The plaintiffs appealed, and in June 2021, the U.S. Court of Appeals for the Ninth Circuit reversed the District Court’s decision, holding that the allegations established that the defendants “knowingly” provided “substantial assistance” to an act of international terrorism because they were cognizant of ISIS using their platforms.

Twitter, Google, and Facebook were all defendants in the District Court and appellees in the Ninth Circuit Court of Appeals. In May 2022, Twitter filed a petition for a writ of certiorari, asking SCOTUS to review the Ninth Circuit’s broad interpretation of the ATA. In October 2022, SCOTUS granted Twitter’s petition.



Anti-Terrorism Act Basics

The Anti-Terrorism Act (18 U.S.C. § 2333), which is part of the U.S. “material support” statutes, allows U.S. persons to sue for any injury caused by an “act of international terrorism” committed, planned, or authorized by an organization designated as a Foreign Terrorist Organization (FTO) under Section 219 of the Immigration and Nationality Act. Any person who aids and abets a terrorist act, by knowingly providing substantial assistance to the FTO, can be liable under the ATA.

To establish liability under the ATA, a plaintiff must prove:

  1. an act of international terrorism committed by an FTO;
  2. an injury to a U.S. person, or their estate, survivors, or heirs;
  3. conduct that “proximately” caused the injury, or secondary liability if the defendant aided and abetted the acts of terrorism; and
  4. intent.

Liability under the ATA through aiding and abetting an act of terrorism was enacted by Congress in 2016 through the Justice Against Sponsors of Terrorism Act (JASTA). Plaintiffs that seek aiding and abetting liability can receive treble damages and the cost of the suit, including attorney’s fees.

Alarmed at the broad interpretation of ATA by the Ninth Circuit, C&SN and InterAction filed an amicus curiae “friend of the court” brief in the case due to the implications for nonprofit organizations (NPOs) working in proximity to terrorist groups. C&SN argued that under a broad interpretation of the ATA, NPOs could potentially be held liable for “aiding and abetting” terrorist acts if any of their aid or services unintentionally end up in the hands of individuals associated with terrorist groups.

On Feb. 22, 2023, SCOTUS heard oral arguments on the case. On May 18, 2023, SCOTUS decided the case and issued its opinion, which ventured to answer two crucial questions to decide whether Twitter was liable under the ATA:

  • What does it mean to “aid and abet?”
  • What precisely must one do to have “aided and abetted?”

What does it mean to “aid and abet”?

To answer the first question, SCOTUS turned to the leading case on aiding and abetting liability, which was also argued extensively in the parties’ briefs and at oral arguments: Halberstam v. Welch.

The facts of Halberstam differ from the facts of this case in several ways. In Halberstam, a “serial burglar,” Bernard Welch, killed Michael Halberstam during a break-in. Halbertsam’s estate then sued Welch’s live-in partner, Linda Hamilton, for aiding and abetting and conspiring with Welch because she was a bookkeeper for his criminal enterprise, and therefore she was a “willing partner” in Welch’s criminal activities. Hamilton was not present when Welch murdered Halberstam, nor were there any allegations that she was even aware of the murder.

In its analysis, the Halberstam court held that in order for courts to find a defendant liable for aiding and abetting, the following elements must be met:

  1. “the party whom the defendant aids must perform a wrongful act that causes an injury;”
  2. “the defendant must generally be aware of [their] role as part of an overall illegal or tortious activity at the time that [they] provide the assistance;” and
  3. “the defendant must knowingly and substantially assist the principal violation.”

Halberstam described six factors for courts to consider in determining whether a defendant’s assistance was “substantial:”

  1. “the nature of the act assisted;”
  2. the “amount of assistance” provided;
  3. the defendant’s presence, or lack thereof, at the time of the violation;
  4. the defendant’s relation to the “tortious actor;”
  5. “the defendant’s state of mind;” and
  6. the “duration of the assistance” by the defendant.

Halberstam also held that individuals who aid and abet may be liable “for other reasonably foreseeable acts done in connection with [the act],” in addition to the act itself.

The Halberstam court found that Hamilton was liable for aiding and abetting under this framework because her bookkeeping activities assisted Welch in a way that “turned his ‘stolen goods’ into ‘legitimate wealth’ thereby intending to help Welch succeed by performing a function crucial to any thief.” [p. 488]

In applying the Halberstam framework to Twitter v. Taamneh, SCOTUS admitted that the allegations of the present case are “a far cry from the facts of Halberstam . . . . its precise three elements and six-factor test thus may not be entirely adequate to resolve these new facts.” [p. 11]. Therefore, SCOTUS ascertained the “basic thrust” of Halberstam’s elements and adapted its framework to this new set of facts, signaling that the leading case on aiding and abetting liability should not be followed strictly, but rather, as Halberstam itself prescribes, be “adapted as new cases test their usefulness in evaluating vicarious liability.” [p. 489]. This is one of the applications where SCOTUS stated that the Ninth Circuit, and the parties to the case, “missed the mark,” stating that the Ninth Circuit too “rigidly” focused on Halberstam. [p. 11].

In determining what it means to aid and abet, SCOTUS also looked to post-Halberstam case law on aiding and abetting, noting that the general gist of aiding and abetting entails just what the ATA requires: “that the defendant have given knowing and substantial assistance to the primary tortfeasor.” [p. 15 emphasis added]. SCOTUS acknowledged that courts have often interpreted these requirements as “working in tandem, with a lesser showing of one demanding a greater showing of the other.” Meaning, less substantial assistance requires more “scienter,” or knowledge of a wrongful act, and vice versa.

SCOTUS thus concluded in Twitter v. Taamneh that “[a]t bottom,” both statute and case law rest on the same “conceptual core that has animated aiding and abetting liability for centuries: that the defendant consciously and culpably ‘participate[d]’ in a wrongful act so as to help ‘make it succeed.’” [p. 17]. Therefore, SCOTUS held that “aids and abets” refers to conscious, voluntary, and culpable participation in another’s wrongdoing.” [p. 17].

What precisely must one do to have “aided and abetted”?

Anyone who “aids and abets, by knowingly providing substantial assistance, or who conspires with the person who committed such an act of terrorism,” can be held liable under the ATA. In its opinion, SCOTUS addresses the arguments by the parties as to whether one must aid and abet the wrongful act itself, or simply the person who then goes on to commit the wrongful act.

The plaintiffs argued that one must only aid and abet the person, therefore making Twitter liable for aiding and abetting ISIS generally, even if there is no indication that Twitter knowingly provided substantial assistance to the Reina nightclub attack. Twitter argued that one must specifically aid the act, and therefore Twitter is not liable because there is no indication of such assistance to the Reina nightclub attack. According to SCOTUS, “[n]either side is quite right.”

SCOTUS held that a defendant must “knowingly provide substantial assistance” to an ”actionable wrong.” It is not enough to allege that a defendant gave substantial assistance to an enterprise without also alleging that the defendant provided substantial assistance to an actionable wrong by that enterprise. [p. 20]. Therefore, it is not enough to allege that Twitter gave substantial assistance to ISIS without alleging that Twitter gave substantial assistance to the Reina nightclub attack.

However, a strict nexus between the assistance and the act is not always required, as SCOTUS reiterated how the bookkeeper in Halberstam was held liable for the wrongful acts of the burglar, Welch, because her assistance was so systematic and engrained in Welch’s enterprise that the wrongful acts of Welch were a “foreseeable risk” of her assistance. [p. 20]. Thus, “remote support can still constitute aiding and abetting in the right case.” Furthermore, a defendant may be liable for aiding and abetting if the support is so “systemic that the defendant is essentially aiding and abetting “every wrongful act committed by an enterprise.” [p. 20]. Read more analysis on SCOTUS’ language about systemic assistance below.

In summary, when answering what it means to “aid and abet” and what precisely one must do to “aid and abet”, SCOTUS decided:

  • To find aiding and abetting liability, a defendant must “consciously, voluntarily, and culpably participate” in another’s wrongdoing in such a way as to help make it succeed.
  • A close nexus between the assistance and the act might help establish liability, but it is not necessarily required if the defendant’s assistance is so “systemic” and “pervasive” that the wrongful act is a ‘foreseeable risk’ of the defendant’s support.

Why Twitter is not liable for aiding and abetting under the ATA:

After determining the above standard for finding aiding and abetting liability, SCOTUS turned to the matter at hand: whether Twitter and other social media companies “gave such knowing and substantial assistance to ISIS that they culpably participated in the Reina attack.” Here, SCOTUS held that they did not.

SCOTUS reasoned that:

  • The plaintiff’s allegations failed to suggest that the defendants “culpably associated themselves” with the Reina attack, participated in the attack as something that they “wished to bring about,” or sought to make the attack succeed. [p. 22].
  • The plaintiffs did not allege that the defendants gave ISIS any “special treatment” or “words of encouragement.”
  • The only affirmative conduct that the defendants took was creating their platforms and “related algorithms to display content relevant to use inputs and user history . . . . the mere creation of those platforms, however, is not culpable.” [p. 23].
  • The plaintiffs rest on the claim that Twitter provided “the infrastructure which provides material support to ISIS.” Id. However, SCOTUS took issue with that claim, stating that the “same could be said of cell phones, email, or the internet generally . . . yet, we generally do not think that internet or cell service providers incur culpability merely for providing their services to the public writ large.” [p. 23, emphasis added].

In regard to the claim that Twitter should have acted more aggressively to stop ISIS from using its platform, SCOTUS would require a “strong showing of assistance” and “scienter.” The plaintiffs failed to make that showing for the following reasons:

  1. The relationship between the defendants and the Reina attack is highly attenuated;
  2. The “arms-length” distance between the platforms’ acts (or failures to act) and the Reina attack;
  3. Plaintiffs identify no duty under the law that would require the defendants to remove ISIS content (and even if there were such a duty, it “would not transform defendants’ distant inaction into knowing and substantial assistance that could establish aiding and abetting the Reina attack”);
  4. Lack of concrete nexus between defendants’ services and the Reina attack; and
  5. The benefit to ISIS was merely incidental to the defendants’ services and general business models. [p. 23-28].

In discussing the nexus factor, SCOTUS noted that this was one of the ways in which the Ninth Circuit went astray. The Ninth Circuit erred in framing the issue of substantial assistance “in general,” when there needs to be a definable nexus between the defendants’ assistance and the Reina attack (absent a showing of “systemic” assistance, as mentioned above). [p. 25]. Under the plaintiff’s theory of “general assistance,” defendants could be held liable for aiding and abetting every ISIS terrorist act committed anywhere in the world. In order to find that kind of aiding and abetting liability, SCOTUS held that plaintiffs must allege that defendants “pervasively” and “systematically” provided “culpable assistance” to a “series of terrorist activities” in a way that could be described as “aiding and abetting each terrorist act.” [p. 25-26]. Here, the plaintiffs did not meet that standard.

SCOTUS noted that a secondary defendant (in this case, Twitter) may be liable for all of a terrorist organization’s actions in the following scenarios:

  1. An individual or group provides “routine services” in an “unusual way,” or;
  2. Provides “dangerous wares”
  3. In a way that could constitute aiding and abetting a “foreseeable terror attack.”

[p. 26].

In those scenarios, courts may find that aid to be more “direct, active, and substantial” than in this case, meaning that plaintiffs may be able to “establish liability with a lesser showing of scienter.” [p. 26]. This again emphasizes that the elements of “‘knowledge” and “substantial assistance” must be considered in conjunction with one another. The “knowledge” requirement cannot be considered separately from “substantial assistance,” as the Ninth Circuit did in its analysis. If there’s less evidence of substantial assistance, then a greater showing of knowledge is required, and vice versa.

Finally, SCOTUS criticized the manner in which the Ninth Circuit approached the six Halberstam factors by regarding them as a “sequence of disparate, unrelated considerations without a common conceptual core.” [p. 28]. The Ninth Circuit “erred in focusing . . . primarily on the value of defendants’ platforms to ISIS, rather than whether defendants culpably associated themselves with ISIS’ actions.” SCOTUS reasoned that had the Ninth Circuit considered all factors as a whole, considering the amount and kind of assistance (the second Halberstam factor) in combination with the fact that the algorithms and platforms were generally available to the internet-using public, then it would have come to the conclusion that “ISIS’ ability to benefit from these platforms was merely incidental to defendants’ services and general business models.”[p. 28]. SCOTUS concluded that “[t]he fact that some bad actors took advantage of these platforms is insufficient to state a claim that defendants knowingly gave substantial assistance and thereby aided and abetted those wrongdoers’ acts.” [p. 28].

In summary, SCOTUS offers “clear guideposts” for finding aiding and abetting liability under the ATA:

  1. The point of aiding and abetting liability is to “impose liability on those who consciously and culpably participated” in the wrongful act.
  2. The focus should be on assistance to the wrongful act for which the plaintiffs seek to impose liability.
  3. A direct nexus between the defendant’s assistance and the wrongful act allows courts to “more easily infer . . . culpable assistance.”
  4. The more “attenuated the nexus, the more courts should demand that plaintiffs show culpable participation through intentional aid that substantially furthered the [act of terrorism].”
  5. If a plaintiff seeks to hold a defendant liable for all wrongful acts of an enterprise, a showing of “pervasive and systemic aid is required to ensure that defendants actually aided and abetted each tort of that enterprise.

[p. 30].

What does this mean for NGOs and civil society operating in areas where terrorist groups are present?

SCOTUS’ opinion offers some assurances to NGOs providing humanitarian assistance or peacebuilding processes to broad populations who are concerned about defending against any allegations that their services would inadvertently support terrorist acts.

In Twitter v. Taamneh, SCOTUS emphasized that “aids and abets” refers to a conscious, voluntary, and culpable participation in another’s wrongdoing . . . . so as to help make it succeed.” [p. 17]. Therefore, to be held secondarily liable under the ATA, NGOs must have “culpably associated” themselves with an act of terrorism as something that they “wish[ed] to bring about.” [p. 22]. SCOTUS underlined several times that general services that are being offered to the public writ large will not result in secondary liability, absent some affirmative conduct, such as “special treatment” or “encouragement” to those committing the terrorist acts. [p. 22]. Therefore, “merely incidental” benefits of general NGO services that are available to the general public should not amount to aiding and abetting liability under the ATA.

While, of course, the ATA continues to leave room for liability for NGOs under the U.S. material support statutes, the language in this case narrows the scope of liability ATA and reverses the dangerously broad interpretation of ATA liability by the Ninth Circuit. While the Court did not explicitly provide for any protection of NGOs in its opinion, C&SN hopes this case will provide assurances and protection to NGOs concerned about highly attenuated and politically motivated claims under the ATA lacking any sort of nexus that ties legitimate NGO activities to terrorist acts.

C&SN will continue to monitor and provide updates on cases under the ATA.