Vegas gunman studied SWAT tactics, music site before attack

Clark County Sheriff Joe Lombardo discusses the Route 91 Harvest Festival mass shooting during a news conference at the Las Vegas Metropolitan Police Department headquarters, Friday, Jan. 19, 2018, in Las Vegas. Lombardo released a preliminary report on the investigation of the shooting that became the deadliest mass shooting in modern U.S. history. (AP Photo/John Locher)

LAS VEGAS — The Las Vegas gunman meticulously planned the worst mass shooting in modern U.S. history, researching SWAT tactics, renting other hotel rooms overlooking outdoor concerts and investigating potential targets in at least four cities, authorities said Friday.