As News Nation reported, Crooks pointed his firearm at the police officer to force him to retreat.

According to NY Post:

After rallygoers spotted Crooks on the roof of a manufacturing plant just 130 yards from the stage where Trump was speaking just after 6 p.m. Tuesday, police were notified and one officer climbed a ladder to investigate, law enforcement officials said on the condition of anonymity.

There the officer encountered Crooks, who pointed his AR-style rifle at them.

The officer then backed down the ladder, and Crooks immediately took aim and loosed eight shots at the former president – grazing him in the ear, killing one bystander in the rally crowd, and gravely wounding two others.

If the report is true, it could explain why the Secret Service snipers held their fire until after Crooks took his shots.

This is a developing story and will be updated when more information is available.