What we know: 5 Dallas police officers killed in sniper attack

A Dallas police officer covers his face as he stands with others outside the emergency room at Baylor University Medical Center in Dallas. Snipers opened fire on police officers Thursday night, killing some of the officers.
A Dallas police officer covers his face as he stands with others outside the emergency room at Baylor University Medical Center in Dallas. Snipers opened fire on police officers Thursday night, killing some of the officers.