March for Our Lives, a student-led movement in support of gun control legislation that formed in response to a 2018 school shooting, is planning a march in the nation's capital in the wake of the mass shooting at Robb Elementary School.

"In 2018 you marched with us to end gun violence. 4 years later, we're marching again," the organization said on Twitter Wednesday evening, announcing a march in D.C. on June 11.

The organization held a march following a shooting at Marjory Stoneman Douglas High School in Parkland, Florida, in 2018 that killed 17 people.

Authorities believe the Uvalde school shooter was shot and killed by a member of the Customs and Border Protection's tactical unit, known as BORTAC, CBP Del Rio Sector Chief Jason Owens told ABC News.

Owens, who did not identify the agent, said his actions "were absolutely courageous," but added it wouldn't be fair to single anyone out.

"It would be unfair to say that any one person's actions were singularly responsible for ending that threat," Owens said. "It took everybody."

-ABC News' Josh Margolin and Mireya Villarreal

As law enforcement officials continue to scrutinize each movement made by alleged gunman Salvador Ramos inside Robb Elementary School, Texas Department of Public Safety Director Steven McCraw said that law enforcement officers shot and killed the suspect roughly 40 minutes to an hour after his first encounter with the school district's resource officer at the building entrance.

"I don’t want to give you a particular timeline. But the bottom line is that law enforcement was there," McCraw told reporters during a briefing Wednesday. "They did engage immediately. They did contain him in the classroom, and they put a tactical stack together in a very orderly way and of course breached.”

McCraw later said that investigators plan to go frame-by-frame through surveillance footage to "track every minute" of the gunman's movement and will provide an update once that work is completed.

-ABC News' Lucien Bruggeman

The suspected Robb Elementary School shooter was not wearing body armor during Tuesday's massacre, multiple law enforcement officials told ABC News.

The alleged gunman was wearing tactical gear, including a vest that could hold ammunition, but there was no armor or fabric that would protect him from gunfire, the sources said.

-ABC News' Matt Gutman, Josh Margolin and Aaron Katersky

The Justice Department will conduct a critical incident review to examine the law enforcement response to last week’s school shooting in Uvalde, Texas, a spokesperson announced on Sunday.

The review is being conducted at the request of Uvalde Mayor Don McLaughlin and the DOJ will publish a report on its findings at the conclusion.

"The goal of the review is to provide an independent account of law enforcement actions and responses that day, and to identify lessons learned and best practices to help first responders prepare for and respond to active shooter events. The review will be conducted with the Department’s Office of Community Oriented Policing," the DOJ said in a statement.

“As with prior Justice Department after-action reviews of mass shootings and other critical incidents, this assessment will be fair, transparent, and independent. The Justice Department will publish a report with its findings at the conclusion of its review.”