In the aftermath of the attempted assassination of former President Donald Trump, authorities are intensifying their investigation into the 20-year-old gunman, Thomas Matthew Crooks, who fired at Trump during a rally in Butler, Pennsylvania. The incident, which left Trump with an injury to his right ear and resulted in the death of one rally-goer, has sent shockwaves through the nation and raised significant security concerns.

A picture obtained by WPXI, a Pittsburgh-area NBC affiliate, revealed a cellphone and detonator found on the rooftop from which Crooks launched his attack. These items were discovered alongside the AR-15-style rifle Crooks used to target the former president. The discovery of these devices has added a new layer of complexity to the investigation, suggesting the potential for a more extensive and premeditated plan.

Law enforcement sources told ABC News that Crooks gained access to the roof by climbing over an air conditioning unit adjacent to the building, dismissing initial reports that he used a ladder purchased from Home Depot. Despite being spotted by witnesses and law enforcement prior to the shooting, Crooks was not confronted until it was too late.

US Secret Service Director Kimberly Cheatle confirmed in an interview with ABC News that local police were present inside the building from which Crooks fired but were unable to prevent the attack. "There was local police in that building - there was local police in the area that were responsible for the outer perimeter of the building," Cheatle said. However, sources indicated that local police were never stationed in the building concerned, highlighting a critical gap in security coverage.

Tom Knight, the Butler Township manager, described the moments leading up to the shooting. "There was a radio transmission indicating that there was a suspicious individual on the rooftop, [and it] was my understanding [that] was our officers' first notification to begin moving towards that building," Knight explained. Officers attempted to reach the roof, but Crooks pointed his rifle at one officer, forcing him to retreat.

The FBI has since unlocked Crooks's phone, but initial examinations have not provided significant insights into his motives. The investigation has also revealed that Crooks had a remote transmitter in his pocket, which may have been intended to detonate two suspicious devices found in his car and one in his home. These devices, constructed in ammunition containers with receivers, are still being analyzed to determine their functionality and intended purpose.

Authorities are exploring whether Crooks's devices were meant to cause significant harm or merely serve as a diversion. Additionally, investigators discovered a tactical vest in Crooks's car, raising questions about why he did not wear it during the attack. Crooks had also told his employer he would return to work the day after the rally, further complicating the understanding of his intentions.

In response to the attack, Pennsylvania State Police stated they provided substantial support to the Secret Service, including 30 to 40 troopers to secure the inside perimeter of the rally venue. However, they emphasized that securing the building outside the perimeter, from which Crooks fired, was not their responsibility.

The shooting incident has not only intensified scrutiny over the security measures at Trump's rallies but also galvanized Trump's image among his supporters. At the Republican National Convention in Milwaukee, Trump, sporting a bandage over his injured ear, received a hero's welcome as speakers celebrated his survival and criticized the attack.

President Joe Biden has called for a de-escalation of political rhetoric in the wake of the shooting. Meanwhile, the investigation continues, with officials seeking to uncover any further details that could shed light on Crooks's motives and prevent future security lapses.