A previous version of this story stated that the student who recorded the incident spoke to Fadel Alkilani. The student did not engage in a conversation with Alkilani. The article has been updated.

On the 20th anniversary of the Sept. 11, 2001, terrorist attacks, Fadel Alkilani stood by a pile of trash bags filled with American flags on a patch of grass at Washington University in St. Louis. Another student approached him from behind, capturing the incident on video.

The video, which was posted to social media later that day, swiftly sparked criticism against Alkilani for allegedly vandalizing a memorial put together by the College Republicans commemorating the anniversary of the attacks that killed nearly 3,000 people.

“WOW: A student senator @WUSTL was caught on video throwing away 2,977 American flags from conservative students’ 9/11: Never Forget Project memorial. Despicable,” the Young America’s Foundation, a conservative youth organization, tweeted Saturday.

The college newspaper Student Life first reported on the incident.

Alkilani, a computer science senior, said he did remove some of the flags from the campus lawn, each of which represented a person killed during the country’s deadliest terrorist attacks. But he told The Washington Post in an email that the clip was taken out of context.

His plan, Alkilani said in an earlier statement, was never to “steal” or remove the small American flags from the area. Instead, he intended to place the plastic bags on the lawn along with statistics “explaining the human cost of 9/11 in the past 20 years,” referring to crimes against American Muslims as well as people killed and displaced in countries invaded by the United States after the 2001 attacks.

“Any memorial of 9/11 that does not contend with these facts is not only incomplete, but it also amplifies pro-imperialist sentiment and actively disrespects those who have died because of American Invasion,” Alkilani said in the statement.

He added: “Muslims such as I have faced fear, harassment, and Islamophobia from those who unjustly use the victims of 9/11 as a political cudgel.”

Now, the university has launched an investigation into the incident, which its chancellor called “reprehensible” and an attack on the free speech of the College Republicans.

“The removal of the flags impeded the ability of individuals to commemorate the lives lost on 9/11 and to process the trauma of that day. … Students have the right to express their viewpoints, but they also have the obligation to respect others’ expressions,” Chancellor Andrew D. Martin said in a statement. The statement did not identify Alkilani by name.

When contacted late Monday, a spokeswoman for the university referred The Post to the chancellor’s statement but did not respond to questions about whether Alkilani would be disciplined.

Nathaniel Hope, a student who was near the memorial on Saturday morning began recording when he saw Alkilani removing the flags and putting them into plastic bags, Hope told The Post in an email.

“I was speechless and offended that a monument dedicated to those who perished in the attacks of 9/11 was being disturbed,” Hope told The Post in an email.

College Republicans president Nick Rodriguez denounced Alkilani’s actions and demanded the student union remove Alkilani from his leadership role for mocking “one of the most somber days in American history.”

“What does it say to be a top American institution, and have yourself represented by a student leader who has no respect for property, campus traditions or the remembrance of thousands of lost lives,” Rodriguez told the college newspaper. His organization did not immediately respond to an email from The Post early Tuesday.

In a statement posted to Instagram, the student union distanced itself from the incident, adding that it did not “endorse or condone” Alkilani’s behavior.

“SU was not involved in organizing or executing Fadel’s protest. … We mourn with students on our campus and those across the country in remembrance of the 2,977 souls lost in New York City, Washington DC, and Shanksville, PA in 2001, and the thousands of first responders who died from health complications in the years following,” the organization said.

Alkilani told The Post that he and his family have received multiple “violent” and “Islamophobic” emails, social media messages and phone calls since the incident became public. Alkilani, who was born and raised in the United States, told The Post in an email that some people have told him to “go back to your own country” and that others have threatened to kill him.

As of early Tuesday, Alkilani’s Instagram and LinkedIn accounts were no longer active.

“The university has taken some measures to ensure my safety, but the official chancellor’s statement has not addressed the harassment and Islamophobia,” he told The Post. “Additionally, several doxing attempts used university social media post replies to direct vitriol, and the university took an exceedingly long time to shut down the comment[s] section.”

The student union in its statement condemned the “Islamophobic rhetoric and slurs” used against Alkilani and other Muslim students on campus.

“It is never right for students to be threatened, [doxed], targeted with hate speech or expelled because of political expression,” the organization said, adding that its executive board is discussing next steps.

Hope told The Post that police collected the bags with the flags and gave them to the College Republicans later that day. By the end of the day, the organization had planted back the flags on the lawn, Hope said.