Watch moment students sheltered in class during shooting

15-year-old freshman Mark Kluska recorded the moment students huddled together and sheltered in their classroom during an active shooter incident at Oxford High School in Michigan. CNN’s Don Lemon explains.15-year-old freshman Mark Kluska recorded the moment students huddled together and sheltered in their classroom during an active shooter incident at Oxford High School in Michigan. CNN’s Don Lemon explains.