From the Orlando Sentinel March 30, 2012 

Moments before George Zimmerman shot and killed Trayvon Martin, the 17-year-old had him pinned to the ground, was beating him and had threatened to kill him, his father told an Orlando television station. 

Robert Zimmerman, 64, of Lake Mary told WOFL-Channel 35 that his son shot Trayvon only after the Miami Gardens teenager knocked him down with a single punch that broke his nose, then got on top of him and kept punching. 

"After nearly a minute of being beaten, George was trying to get off the concrete, trying to move with Trayvon on top of him into the grass. In doing so, his firearm was shown. Trayvon Martin said something to the effect of, 'You're going to die now,' or, 'You're going to die tonight,' ... At some point, George pulled his pistol and did what he did," Robert Zimmerman said. 

The screams for help heard in the background of one 911 tape, he said, are his son. Critics have said they were the cries of Trayvon, begging for his life.