reporter: shots fired during the lunch hour at the video colossus youtube. the upturned chairs, the bullet casings and the police emergency calls. active shooter at 901 cherry. reporter: now tragically familiar, but not this a female suspect. so, confirming she is the suspect? affirmative, what we were told. we did locate a victim with a what we believe to be a self-inflicted gunshot wound. it s a female. but the investigation is still ongoing. reporter: this is believed to be the first mass shooting by a female since at least 2010. law enforcement sources say the shooting appears to be the result of a domestic situation. the first call came in at 12:46 local time. two minutes later, police arrive. they re in formation as they move up that staircase. this is crazy. we re on lockdown. reporter: inside youtube, employees witnessing the violence. one product manager writing on twitter, i looked down and saw drips of blood on the floor and stairs. upon arrival, of