Seattle Times:

Police spokeswoman Renee Witt said the officer was driving his patrol car south on Boren Avenue near Howell Street about 4:15 p.m. when he saw a man holding a knife who was seated on a short wall on the northwest corner of the intersection. The man appeared to be whittling a piece of wood, Witt said.

The officer, who thought the man was acted strangely, stopped his patrol car and got out, Witt said.

The man stood up and approached the officer, ignoring several orders to stop. At that point, the officer opened fire, she said.

UPDATE: also has more details.