According to reports, there were three police snipers in the building from which the shooter fired

Three police snipers were stationed inside the building and tasked with watching the rally from the window, CBS News and local broadcaster Beaver County reported, citing local law enforcement sources.

One of the police officers stationed in the building saw the shooter “scouting” the roof with a rangefinder before briefly disappearing from the scene and returning with a backpack, reports said.

The officer managed to take a photo of the shooter and even radioed the sightings to his dispatch center, but the suspected shooter, 20-year-old Thomas Matthew Crooks, reportedly managed to climb onto the roof through an air conditioning unit.

Local police officials quoted in the reports blamed their failure to combat Crooks on a lack of manpower – which meant they could not post a sniper on the roof or assign scouts to accompany the snipers on the ground – and “extremely poor planning.”

According to local television station WPXI, Crooks was discovered by officers on the scene nearly 30 minutes before he shot at Trump and the rally attendees.