The congressional committee investigating the January 6, 2021 attack on U.S. Capitol on Tuesday detailed how former President Donald Trump used Twitter to incite his violent followers ahead of the deadly incursion—and how the social media giant helped foment the insurrection.

An anonymous former Twitter employee said in recorded testimony that they had tried in vain to persuade company officials to take action amid growing calls for violence following incendiary tweets by Trump. These include December 19, 2020 posts in which Trump encouraged supporters of his “Big Lie” that Democrats stole the presidential election to rally in Washington, D.C. on January 6, 2021.

“Be there, will be wild,” said one Trump tweet. “This could get out of control,” said another.

In recorded testimony, the witness said that Trump “was speaking directly to extremist organizations and giving them directives. We had not seen that sort of direct communication before.”

“I came to the reality,” the former Twitter employee added, that if the company “made no intervention into what I saw, people are going to die, and on January 5th I realized that no intervention is coming.”

Another witness, convicted January 6 insurrectionist Stephen Ayres, testified in person that the Capitol attackers were “basically just following” what Trump said, and that the seditious mob began to disperse after the president asked them to leave the building.

While Twitter permanently suspended Trump’s account two days after the deadly Capitol attack, the former employee testified that company leaders knew for some time that his tweets were inciting violence.

“Twitter relished in the knowledge,” they said, “that they were also the favorite and most used service of the former president and enjoyed having that sort of power.”

Lisa Gilbert, executive vice president of Public Citizen and co-chair of the Not Above the Law Coalition, said in a statement that “Trump’s intimate ties to far-right extremist groups were a cornerstone of his presidency” and that the former president “harnessed the organized anger and venom of these groups to form a mob.”

“The evidence of coordination between Trump, other MAGA Republicans, and white nationalist groups like the Proud Boys and the Oath Keepers who led the assault on the Capitol was masterfully explained,” she continued, adding that “Trump and his allies understood, planned, and marshaled the building blocks for the physical violence.”

Calling Trump’s words “carefully chosen” and his actions “premeditated,” Stand Up America founder and president Sean Eldridge said that “after it became clear that his illegal scheme to overturn the 2020 election was failing, President Trump took to Twitter to summon thousands of violent extremists to the nation’s capital with the express purpose of obstructing the peaceful transfer of power.”

Other observers focused on the role of social media companies like Twitter in abetting the insurrection.

“Today’s shocking whistleblower testimony confirms what many of us have known for years: Big Tech has repeatedly failed to rein in calls to violence on their platforms,” said Nora Benavidez, senior counsel and director of digital justice and civil rights at Free Press.

“We need to view the entire testimony from this former Twitter employee so we can fully understand the company’s role in fomenting the kinds of violence that threatened to overthrow democracy in the United States and seat an authoritarian regime in its place,” Benavides continued. “Twitter—and other social media companies—must stop shirking responsibility, especially as the country prepares for another national election.”