The Supreme Court justices on Wednesday appeared skeptical that Twitter could be held liable for aiding and abetting a 2017 terrorist attack in a lawsuit brought by the relatives of one of the victims.

The case, Twitter v. Taamneh, arose after an ISIS-linked attacker killed Nawras Alassaf and 38 other people at an Istanbul nightclub. Alassaf’s family sued Twitter and other tech platforms, accusing them of not taking enough enforcement action against the terrorist group.

Wednesday’s oral argument wrapped up a double-header for Big Tech at the high court this week that began with Google attempting to fend off a similar suit brought by another ISIS attack victim’s family.

Google asserted that Section 230 — a controversial liability shield for internet companies — protects the company from the underlying terrorism claims.

If the justices ultimately rule in favor of Twitter in the second case, they wouldn’t need to touch the Section 230 question in Google’s dispute because the company wouldn’t need the protections in the first place.

Wednesday’s oral argument probed whether a violation of the anti-terrorism law requires knowingly providing substantial assistance to a specific act of terrorism — as Twitter argues — or if the court should follow the family’s contention that assistance to ISIS’s broader criminal enterprise suffices.

The attacker was never alleged to be on Twitter, but Alassaf’s family’s suit accuses Twitter and other platforms of aiding and abetting the attack by contributing to ISIS’s growth and not taking more aggressive enforcement action against pro-ISIS content.

“The fact that you are focused on the infrastructure rather than specific conduct or specific accounts, does that also mean that Twitter could be held liable — Twitter is an aider and abettor in every terrorist act?” Justice Clarence Thomas pressed Eric Schnapper, who represented the family.

Seth Waxman, who represented Twitter, said holding the platform liable would require alleging that Twitter was aware of specific pro-ISIS accounts or posts but refused to take them down.

“Where the alleged culpable conduct is the failure to do more to prevent misuse of widely available services offered to the world at arm’s length, subject to enforced policies against terrorist content, it is not, as a matter of law, the knowing provision of substantial assistance to an act of international terrorism, absent specific knowledge of specific accounts or posts that were used to plan, commit or proximately support the act of international terrorism that injured the plaintiff,” Waxman said.

Schnapper, on the other hand, asserted that a plaintiff doesn’t need to provide a specific account for their claims to move forward.

“We do not think that the Federal Rules of Civil Procedure require that,” he said.

Justice Neil Gorsuch, who participated remotely because he was feeling “under the weather,” repeatedly stressed the family’s allegations would have to connect to the particular terrorist in question.

“There are very few points in this complaint that they aided the person who engaged in the terrorist attack,” Gorsuch said. “We all appreciate how horrible the attack was, but there’s very little linking the defendants in this complaint to those persons.”

Some of the justices raised concerns about how a broad interpretation of liability could be used in other contexts.

Justice Brett Kavanaugh asked Schnapper if adopting his argument meant CNN could be held liable for its famous 1997 interview with Osama bin Laden, when bin Laden declared war on the United States.  

Thomas, one of Kavanaugh’s fellow conservative justices, asked if a pager company could be held liable for a terrorist that uses its product. Justice Samuel Alito, another conservative, pressed whether companies that manage phone booths could be held liable if a terrorist places calls using their booth.

The Biden administration expressed similar concerns as they argued in support of vacating the lower court decision that favored the family.

“The statute and we are concerned about not extending it so far that legitimate business activities could be inhibited, that banks, for example, in underdeveloped parts of the world and charities that may depend on those banks, concerns about how they may pull back as a result of legitimate businesses,” said U.S. Deputy Solicitor General Edwin Kneedler.

Liberal Justice Elena Kagan pressed Kneedler on banks in particular, asking him whether one could be held liable if bin Laden walked in and opened an account.

“I would be shocked if the government gave that one away, right,” Kagan said.

Kneedler agreed in that scenario, but he stressed that the bank in other hypotheticals could only be held liable if certain conditions are met.

“Somebody who is a leader or somebody who you know has committed or is about to commit a terrorist act,” Kneedler said.