Explained | How the Trump rally gunman had an edge over the counter snipers

The would-be assassin who opened fire at Donald Trump's campaign rally in Butler, Pennsylvania, on July 13 was able to get a clear shot at the former president.

The New York Times used drone photography to build a 3D model and re-create the lines of sight for both the gunman, Thomas Matthew Crooks, and three teams of counter snipers -- two federal and one local.

The analysis shows that Crooks, 20, who flew a drone to survey the site the morning of the rally, exploited one of the few blind spots within a rifle's range of Trump, raising questions about serious lapses in security planning for the event.

Kimberly A. Cheatle, the Secret Service director, resigned last Tuesday, a day after declining to answer lawmakers' questions about sight lines and security breakdowns at a contentious hearing on Capitol Hill.

What Secret Service counter snipers on the North Barn saw

The gunman was largely concealed by two trees and the slope of a warehouse building roof, which he used as his perch. The warehouse complex, owned by AGR International, was outside the Secret Service's designated security perimeter, the agency later said.

Stationed on the northernmost barn behind Trump, one of the Secret Service teams had been facing the gunman's direction for 30 minutes before violence erupted, according to videos posted on social media and verified by the Times. At one point, team members can be seen standing up and looking in the gunman's direction with binoculars.

The Times used a spatial technique called viewshed analysis to calculate what areas would have been visible from the northern counter sniper team's position, taking into account obstructions like trees and buildings. The analysis confirmed that Crooks chose a prime spot that allowed him to stay largely out of sight -- even from a counter sniper team that had been facing his direction for a length of time -- as he prepared for the first shot.

A second Secret Service counter sniper team was positioned on the roof of a barn farther to the south and west. It had been monitoring a different area -- initially facing away from the gunman, videos posted to social media show.

Video footage shows the counter snipers later turning toward the gunman's direction 1 minute and 35 seconds before the first shot was fired.

But the slope of the warehouse roof that the gunman had chosen would have also made it difficult for the south counter sniper team to see him as he crawled upward, a Times analysis shows.

Only the very top of Crooks' head would have been visible in either Secret Service counter sniper team's line of sight, or only while the gunman was hunkered behind the highest point on the roof.

Forty-two seconds after the shooting began, Secret Service agents can be heard saying "Shooter down" in video footage. Crooks was fatally shot by a Secret Service counter sniper, the agency later confirmed. It's likely the shot came from the counter snipers on the south barn, who would have been one of the best positioned.

What the gunman saw

The gunman's spot on a warehouse roof -- less than 500 feet from Trump -- provided him with a clear, elevated line of sight.

Investigators said that Crooks used a drone to survey the rally site before the shooting. The Secret Service did not seek to use drones to provide agents with aerial views of the rally, Cheatle testified last Monday.

Crooks was able to fire multiple shots -- unimpeded -- in Trump's direction, injuring Trump's right ear. A rally attendee sitting in the bleachers closest to the gunman was fatally shot in the head. Two others in the top row of bleachers to the south were also struck, though they survived.

What local law enforcement counter snipers saw

A third group of three law enforcement counter snipers was stationed in the same warehouse complex as the gunman, but in an adjacent building, according to a local law enforcement official, who was not authorised to comment.

The building that the counter snipers were in did have windows facing the side of the roof of the building that Crooks climbed up. But it is not known whether they were assigned to any of those windows that day.

The law enforcement official said the counter snipers, who were tasked with watching over the crowds, were positioned on the other side of the building, at the second-floor windows farther from the gunman.

From this view inside the building, the gunman would have been out of the counter snipers' lines of sight.

Videos and photos reviewed by the Times show what was most likely a fourth counter sniper team from a local law enforcement agency roughly 1,000 feet from Crooks' position on the roof.

The team was visible several times in the hours and minutes before Trump began his speech. The Times could not confirm whether the team fired at any point during the shooting.

Other security missteps

Two rows of chain-link fencing divide the Butler Farm Show property from the warehouse complex. It's unclear if the Secret Service used the fencing to delineate the security perimeters, but the agency later acknowledged that the AGR warehouses were excluded from the secure zone.

The warehouse complex, which sits next to a state highway and a major road, is accessible to the public. In a video taken an hour before the shooting, Crooks can be seen in front of the warehouse building he would later use as his perch.

On the ground, dozens of officers from multiple agencies were also present on the Butler Farm Show grounds, where the rally took place. Cheatle said last Monday that the AGR building complex was being monitored at the time of shooting, but she did not specify by whom.

An FBI investigation had found that a local SWAT team spotted Crooks on the roof of a warehouse approximately 18 minutes before Trump took the stage, Cheatle also said at last week's hearing.

The Secret Service had been informed of a potential "suspicious" person through radio communication, but it did not stop Trump from taking the stage.

Methodology

The Times flew a drone July 16 over the site of the attempted assassination of Trump in Butler and used the imagery captured by the drone to create a 3D model of the scene.

The Times also used measurements collected on the ground, satellite imagery and references from photos and videos posted on social media to corroborate the dimensions in the model.

The positions of the gunman, counter sniper teams and the victims were based on sites the Times located from social media videos.

To determine the lines of sight of each counter sniper team in the 3D model, the Times conducted a viewshed analysis -- a spatial technique used to calculate what areas would be visible from a specific location in 3D, taking into account obstructions.

The Times used a 1,000-foot radius from the position of the counter snipers for this analysis, which encompassed both the Butler Farm Show grounds and the AGR warehouse complex.

The Times placed cameras in the 3D model at the approximate locations of the gunman's and the counter sniper teams' elevations to show what their views might have looked like from those vantage points.

The gunman's exact location in the renderings is based on the position where his body was found after he was shot. The specifics of the scopes used by the gunman or the countersnipers on their rifles are not known, and the 3D renderings are approximate.