On Tuesday afternoon there were reports of an active shooter on the campus of YouTube in San Bruno. In the moments after a potential mass shooting it can be hard to know what has happened, even as first responders, witnesses, and journalists scramble to piece together the truth. Today, we follow KQED reporters in the hours following the gunfire. Guests: KQED Silicon Valley Editor Tonya Mosley and KQED Silicon Valley Reporter Sam Harnett. Subscribe to The Bay