The Boulder police chief says two officers who shot and killed a man wielding a machete at the University of Colorado were trapped in a stairwell with him and fired after he refused to drop the knife and advanced toward them.

The Daily Camera reports that Chief Greg Testa provided the details during a city council briefing on police force Wednesday. The shooting is still being investigated by authorities from around the county.

Testa said the officers -one from Boulder police and one campus officer - were trying to back down the stairs at the university's athletic complex as they were yelling at the man, former Marine Brandon Simmons. He says Simmons was trying to access the fifth and sixth floors which require a key card. He says neither Simmons nor the officers had one.