FBI examines Trump assassination attempt suspect's phone, transmitter found on him

Authorities said the man they allege tried to assassinate former President Donald Trump was able to access the roof near the rally by climbing over an air conditioning unit adjacent to the building, sources told ABC News.

Though law enforcement sources said Thomas Matthew Crooks is believed to have purchased a 5-foot ladder at a Home Depot before the shooting, it does not appear to have been used to climb on the roof and was not found at the scene.

As the FBI investigation continues, questions are swirling about how the 20-year-old was able to ascend undetected to the roof, gain a direct line of sight and fire several rounds at the former president. The alleged gunman's motive was also still unclear as the investigation continue Wednesday. Crooks was killed at the scene, the Secret Service said.

Investigators said Tuesday they found a remote transmitter in the suspect's pocket that may have been intended to set off two suspicious devices found in the suspect's car and one in his home, according to law enforcement sources. Devices at both locations were similarly constructed in ammunition containers using components including receivers that appear to have been paired with the remote control found in the suspect's pocket, sources said.

The receivers in each device were connected to a series of components that investigators say met the "eye test" -- having parts present that could have made viable devices, although the functionality of the devices is still being determined. The purpose of the devices is also unknown. Whether they were intended to cause a significant blast effect and hurt people or if they were designed to create smoke, fire and a low-grade blast for a diversion is unclear.

Investigators also found a tactical vest in the suspect's car, though it is unclear why he did not wear it during the assault on the former president's rally. Some investigators are wondering whether he anticipated dying in the attack.

The shooter also asked his employer if he could take a day off on Saturday but said he would return to work perhaps as soon as Sunday, the day after this attack, according to law enforcement sources. But thus far, investigators have turned up nothing to suggest that he had any accomplices or other support to carry out his deadly objective.

An examination of his phone, which the FBI has now unlocked, has not turned up any significant information about the suspect's motives -- only what sources described as "routine" information for a 20-year-old male. Thus far, investigators have turned up nothing to suggest that he had any accomplices or other support to carry out his deadly objective.

The Pennsylvania State Police said in a statement that it provided "all resources" to the Secret Service -- including 30 to 40 troopers to assist with securing the inside perimeter of the campaign rally venue in Butler Township, Pennsylvania -- but "was not responsible for securing the building or property" outside the security perimeter where the would-be assassin opened fire.

In an exclusive interview with ABC News , U.S. Secret Service Director Kimberly Cheatle confirmed that local police were present inside the building at the same time the shooter was on the roof firing at Trump. Cheatle also said that local authorities were tasked with securing that building.

"In this particular instance, we did share support for that particular site and that the Secret Service was responsible for the inner perimeter," Cheatle said. "And then we sought assistance from our local counterparts for the outer perimeter."