An inside look at everything that went wrong and how a would-be assassin was able to put Trump in his bullseye

Failed communication between the Secret Service and local law enforcment heavily contributed to lapses in security

New details about the hours leading up to the Trump rally shooting show gaping holes in the Secret Service’s security detail that allowed a 20-year-old gunman to have a clear shot at Donald Trump and a crowd of his supporters.

Several reports depict a stunning lack of communication between law enforcement officials and Trump’s team members about a suspicious man who managed to make his way to the top of a nearby building.

Though members of the local Beaver County SWAT team spotted the young man- later confirmed to be the gunman Thomas Matthew Crooks - they apparently had no contact with Secret Service agents assigned to protect the former president.

Other law enforcement agencies missed several opportunities to catch the gunman once he was spotted. The Secret Service failed to include the nearby building as part of the security zone.

Ultimately, the lapses gave the gunman a chance to fire, killing one person and injuring three others, including the former president. The aftermath, including the former president being grazed by the bullet, left the SWAT team shaken and it’s a memory they’ll carry for the rest of their careers.

“This one is something that we’ll always carry with us,” assistant Beaver County SWAT leader Mike Priolo told ABC News.

Here is what we know so far about the lead-up to the shooting and the security failures:

Lapse in security zone judgment

Before Trump was set to take the stage in Butler, Pennsylvania, the Secret Service assigned local law enforcement agents to post up on several buildings around the rally area. But crucially, they excluded the warehouse building north of the stage where the gunman would later shoot from, according to The New York Times.

This was despite the warehouse being approximately 450 feet from the lectern where Trump spoke – well within the range that an AR-15-style rifle can shoot from.

The decision ultimately allowed Crooks to get onto the roof of the building and set up his shot.

Police snipers return fire after shots were fired while Republican presidential candidate former President Donald Trump was speaking at a campaign event on July 13. Before Trump was set to take the stage in Butler, Pennsylvania, the Secret Service assigned local law enforcement agents to post up on several buildings around the rally area. But crucially, they excluded the warehouse building north of the stage where the gunman would later shoot from. (AP)

Additionally, the Secret Service’s decision to assign local law enforcement to monitor the perimeter left local law enforcement officers tasked with the daunting duty of visually scanning individuals walking into the rally.

“Our first indication that there was going to be something different about this was the lack of patrol that we’d seen in the area,” Beaver County Chief Detective Patrick Young told ABC News.

Young said officers had to quickly decide if rallygoers carrying something in their pocket was water, booze or a potential weapon. Priolo told the news network that, “The best analogy I’ve heard is -- we’re a scalpel, when you’re asking us to be used as a hammer.”

In the aftermath of the shooting, Priolo said it’s, “something that we’ll always carry with us.”

Little to no communication between Secret Service and local law enforcement

Officials of the local Beaver County SWAT team told ABC News that they never had a meeting with Secret Service agents when they arrived at the rally site – something that contributed to an overall lack of communication.

The Beaver County SWAT was tasked with supporting the Secret Service and other law enforcement agencies as the rally went underway.

"We were supposed to get a face-to-face briefing with the Secret Service members whenever they arrived, and that never happened," Jason Woods, the team leader for Beaver County’s Emergency Services Unit and SWAT sniper section, said.

Without a way to contact each other, local law enforcement was unable to quickly inform Secret Service agents that they spotted Crooks acting suspiciously, nearly 100 minutes before the rally began.

Two FBI investigators scan the roof of AGR International Inc, the building adjacent to the Butler Fairgrounds, from where shooter Matthew Thomas Crooks fired at Trump. Local SWAT has now detailed a lack of communication with Secret Service agents. (Getty Images)

Gregory Nicol, a Beaver County SWAT sniper, said he spotted Crooks wandering near the buildings around the rally location with a backpack and rangefinder. Nicol took photos of the young man and flagged him to his colleagues.

“It just didn’t seem right,” Nicol told ABC News.

He would be the first to alert his colleagues about the suspicious individual, who later turned out to be the gunman.

Text messages, seen by The New York Times, show the snipers exchanging messages with each other about Crooks – warning of his activity, flagging his movements and escalating concerns about his whereabouts.

One sniper texted his colleague alerting him that Crooks was keeping tabs on their movements.

“He knows you guys are up there,” the sniper wrote at 4:26 p.m. – nearly an hour and a half before the shooting occurred.

Another text went out a half-hour later when a countersniper asked his colleagues to inform the Secret Service of Crooks’ movements. He sent photos to the group chat of Crooks as well.

Trump is rushed offstage by Secret Service agents after being grazed by a bullet during a rally. There have been numerous reports about how the shooter was spotted well before he opened fire (Getty Images)

But the sniper team was unable to contact the federal agency until after the tragic shooting.

Members of Trump’s team have allegedly privately expressed frustrations that they were made unaware of any suspicious activity before the rally, according to the Washington Post. 

Kimberly Cheatle, the director of the Secret Service has resigned in the aftermath of the shooting.

Missed opportunities to catch the gunman

It wasn’t just the team of snipers who discovered Crooks before he opened fire – local law enforcement officers saw him on the roof and bystanders shouted about him wielding a gun.

After the team lost track of Crooks’ whereabouts, officers from the Butler Township Police Department, who were initially assigned to direct traffic near the warehouse, tried to find the gunman minutes before the shooting.

Two officers went to the warehouse rooftop and one hoisted the other one up so he could see above the roofline. It was there that the officer saw Crooks with his firearm, Edward Natali the Butler Township Commissioner told Fox News.

“The suspect turned his rifle on that officer,” Natali said.

Crooks was identified by the FBI as the shooter involved in an assassination attempt of Trump (AP)

But the officer was holding onto the roof and unable to retrieve his own firearm he fell backwards, injuring himself.

Seconds before Crooks opened fire, people on the ground spotted Crooks on the rooftop and shouted at law enforcement officials to get their attention. Videos posted online show the people directing officers to the warehouse rooftop.

At that point, it was too late.