The father of the teenager accused of killing two students and two teachers at a suburban Atlanta high school defended himself on the stand, saying he didn’t see warning signs that his son could kill. ---- Subscribe to ABC News on YouTube: https://abcnews.visitlink.me/59aJ1G ABC News Digital is your daily source of breaking national and world news, exclusive interviews and 24/7 live streaming coverage. Download the ABC News app for the latest headlines and alerts: https://abcnews.go.com/devices