Complex sentence: Zimmerman later claimed in testimony that Apperson approached him over a rear tire leaking air, which Zimmerman was already aware of and explained this to Apperson before he asked Zimmerman if he knew he was "wrong for killing that little black boy".
Split into simpler sentences: Zimmerman later claimed in testimony that Apperson approached him over a rear tire leaking air, which Zimmerman was already aware of. He had explained this to Apperson before he asked Zimmerman if he knew he was "wrong for killing that little black boy".