Student activist Emma González led an emotional moment of silence at the "March for Our Lives" rally in Washington Saturday. The moment of silence lasted for 6 minutes and 20 seconds -- the duration of the gunman's rampage in Parkland, Florida. Chin high and tears streaming, González stood silent in front of thousands gathered for the event.

After calling out all 17 students' names, she led a long moment of silence that concluded her first 6 minutes, 20 seconds on stage.

She continued standing silently as a few crowd members shouted out support. She remained silent as tentative chants broke out. Her silence continued as those attending also fell quiet, many weeping.

"Since the time that I came out here, it has been 6 minutes and 20 seconds, the shooter has ceased shooting and will soon abandon his rifle and blend in with the students so he can walk free for an hour before arrest," González said, breaking her silence. "Fight for your lives before it is someone else's job."

González is one of several teens from Marjory Stoneman Douglas to become gun control activists in the wake of the shooting. Their efforts have galvanized youth nationwide, with hundreds of thousands attending similar rallies across the country.

González wrapped up the rally with some homework for those who demonstrated nationwide. "One final plug," she said. "Get out there and vote."

Over the past five weeks, after the murders of 17 people at the high school, CBS News has followed the students as they started a movement. It's all featured in CBS News' documentary "39 Days." You can watch the one-hour documentary here.