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local LE was alerted about the shooter prior to the event
Sledog
Member Posts: 34,253 
in Tug Tavern
The U.S. Secret Service said Sunday that local authorities were alerted to a threat ahead of the Trump Rally in Butler, Pennsylvania on Saturday, but could not find the gunman in time.
Local law enforcement was alerted to a suspicious individual by attendees but could not locate Mr. Crooks before he climbed onto the roof and opened fire, according to US Secret Service Spokesman Anthony Gugliemi.
Mr. Guglielmi tells Fox News the first time Secret Service agents saw the gunman he was already on the roof firing.
At that point, “ a Secret Service Counter Sniper neutralized him,” Guglielmi said.