Santa Barbara County Sheriff Bill Brown showed off a road map of Friday night's mass murder in Isla Vista and identified the killer as 22-year-old Santa Barbara City College student Elliot Rodger.
Deputies carried out a large poster showing 10 locations and more than a dozen crime scenes.
Brown described six murders and more than a dozen injuries.
He said the first slayings were not followed by a 911 call.
Deputies showed photographs of handguns Rodger legally purchased in Goleta, Oxnard and Burbank.
Officers did a welfare check on Rodger late last month but did not find a reason to enter the apartment.
The Sheriff said he was aware of "chilling" You Tube videos posted by the killer and a 141 page autobiographer and diary he titled My Twisted World.