Complex sentence: At approximately 5:00 a.m. police shot and killed Mateen, ending the attack, but not after Mateen had killed at least 50 people and injured 53 more.
Split into simpler sentences: At approximately 5:00 a.m. police shot and killed Mateen, ending the attack. In the end, Mateen had killed at least 50 people and injured 53 more.