The 20-year-old who attempted to assassinate former President Trump at a July 13 rally in Butler, Pennsylvania, "carefully planned" and scoped out the Butler, Pennsylvania, rally-sight, the FBI revealed on Monday.

"We believe the subject made significant efforts to conceal his activities," FBI officials said during a conference call.

The FBI said that Crooks engaged in "careful planning ahead of the campaign rally" prior to the fateful Trump rally that left one dead and three injured, including the former president.

Crooks' meticulous planning included visits to the rally sight, the Butler County Fair Grounds, a week prior to the shooting.

The 20-year-old also went to a shooting range the day before the attack to practice with the same weapon he used in the attack, authorities said.

TRUMP SHOOTING: TIMELINE OF ASSASSINATION ATTEMPT RAISES QUESTIONS ABOUT HOW GUNMAN EVADED SECURITY

Undated file photo of Thomas Matthew Crooks

Thomas Matthew Crooks is alleged to be the shooter in the assassination attempt on former President Donald Trump in Butler, Pennsylvania, on Saturday, July 13, 2024. (Obtained by Fox News Digital)

The FBI revealed that Crooks' father, Matthew Brian Crooks, legally transferred a DPMS AR-15-style firearm with a collapsible stock to his son – the same firearm that the 20-year-old used in the shooting.

It was purchased legally by the shooter's father in 2013, according to the FBI.

TRUMP ASSASSINATION ATTEMPT: TEXTS REVEAL OFFICERS WERE AWARE OF THOMAS CROOKS 90 MINUTES BEFORE SHOOTING

The federal agency also revealed that Crooks stockpiled guns as well as components to create explosive devices.

The FBI said that in spring 2023, over a year prior to the shooting, Crooks made 25 gun purchases using online aliases. 

An evidence photo of a cell phone and transmitting device found alongside Thomas Crooks

An evidence photo of a cell phone and transmitting device found alongside Thomas Crooks after his attempted assassination of former President Donald Trump in Butler, Pennsylvania, on Saturday, July 13, 2024.  (Provided by Senator Chuck Grassley )

The parents of former president Donald Trump's assassin arrive home

The parents of Thomas Crooks, Matthew and Mary Crooks, return to their home in Bethel Park, Pennsylvania, on Wednesday, July 24, 2024. Mary Crooks has not been seen in public since her son attempted to assassinate former President Trump on July 13 in Butler, Pennsylvania. (Derek Shook for Fox News Digital)

In the first half of 2024, the FBI said, he made six chemical precursor related purchases of material used to create explosive devices.

Crooks' parents said that their son had a keen interest in science and had always done experiments, so the parents were not alarmed when the packages began to stack up at their modest home in Bethel Park, Pennsylvania.

Law enforcement officers stand over the body of would-be Trump assassin, Thomas Crooks on the roof of a building

Law enforcement officers stand over the body of would-be Trump assassin, Thomas Crooks, on Saturday, July 13, 2024.  (Todd the Driller)

Kevin Rojek, FBI Special Agent in Charge of the Pittsburgh field office, said officers are still investigating Crooks' motive after conducting more than 450 interviews and examining more than 2,100 tips from the public.

TRUMPF RALLY SHOOTING VICTIMS' FAMILIES BREAK SILENCE, THANK COMMUNITY FOR ‘OUTPOURING OF SUPPORT’

The agency said that they had requested information from 86 companies connected to Crooks. The FBI did not specify what they requested from the connected companies.

A map detailing the locations of interest pertaining to the investigation of Thomas Crooks' attempted assassination of former President Donald Trump

A map detailing the locations of interest pertaining to the investigation of Thomas Crooks' attempted assassination of former President Donald Trump in Butler, Pennsylvania, on Saturday, July 13, 2024.  (Provided by Senator Chuck Grassley )

The FBI described Crooks as "highly intelligent, attended college and maintained steady employment." They noted that they believe the 20-year-old was a loner.

They said that there has not been any evidence of mental institutions or medications used by Crooks.

The Butler Fair Grounds, approximately the weeks following the shooting, were preparing to launch their county-wide fair.

The Butler Fair Grounds, approximately the weeks following the shooting, were preparing to launch their county-wide fair. (Sarah Rumpf-Whitten/Fox News Digital)

Nearly three weeks following the shooting that rocked the Western Pennsylvania county, the fair grounds launched into preparing for their annual Big Butler Fair.

CLICK HERE TO GET THE FOX NEWS APP

There were no FBI agents on the scene, but Fox News Digital spotted vendors entering and exiting the fair grounds that were open to fair participants to prepare for the county-wide bash.

Fox News Digital has reached out to the FBI for comment.