Its a tragedy, but this seems to be the fault of the bicyclist and/or Washington laws on where and how you can bicycle.

From the accounts, the red don-t walk signal was flashing - its white for walk (which is just ON and doesn't flash) and a red for don't walk (which is flashing before it goes to solid).  One is NOT allowed to begin crossing after the flashing starts.  Many people routinely think they can start crossing if the don-'t walk is flashing - and they are wrong.  That flashing is only to tell the folks already in the crosswalk to hurry up as the light will change shortly for the cross traffic.

Additionally, riding a bicycle into a crosswalk is a bad idea because motorists are expecting pedestrians , and the speed they arrive at, not bicycles.  So riding into a crosswalk increases your chance of surprising other road users and getting into an accident.  Not sure if the law allows riding vs walking a bike across a crosswalk.  The whole concept of biking on a crosswalk is bad.