A week before the shooting, Thomas Matthew Crooks searched online for the date of the Democratic National Convention and where Trump planned to speak, as well as other searches for Trump and President Joe Biden.
These details were among those shared by FBI and US Secret Service officials in a Wednesday briefing with lawmakers and by additional people familiar with the investigation. The previously unreported readout documents the scope of the investigation, including an expanded timeline of the would-be assassin's actions leading to up his assault and law enforcement's failure to prevent it.
ALSO SEE: James Crumbley told son there were 'people you can talk to' in meeting before shooting
Investigators remain puzzled about possible motives for Saturday's attempted assassination of the former president, finding little to point to political or ideological intentions for the attack.
But the would-be assassin's recent trail on the internet has provided investigators with a detailed picture of his possible mindset before the attack. FBI behavioral experts are building a profile of Crooks based on the findings, the FBI told lawmakers.
One emerging theory by investigators, based in part on the timing and subjects of his online searches, is that the shooter was looking to carry out a mass shooting and that the Trump event's proximity and timing offered the most ready opportunity, according to a US official briefed on the matter.
Unlike other mass shooters who often leave behind manifestos or writings to explain their attack, Crooks left behind few clues, in his bedroom or online.
New insight into the final moments of Thomas Matthew Crooks, Trump's would-be-assassin
Investigators recovered rudimentary explosive devices from his car, along with a bullet-proof vest, additional magazines of the type he used in the attack and a drone, according to the officials who briefed lawmakers Wednesday. At the family home, they also recovered 14 firearms and additional explosives, along with a second cellphone, a laptop and hard drive.
Investigators have focused on Crooks' online activity in the months and days before the attack. Family members and people he worked with described him as quiet and a loner but haven't indicated that he showed any signs of planning an attack. In April, he searched websites for information on major depressive disorder and depressive crisis treatment.
On his primary cellphone, investigators found an image of the arrest photo of Ethan Crumbley - the student who shot and killed four classmates at a Michigan high school in 2021 - along with information about Crumbley and his parents, who were both found guilty of involuntary manslaughter, the first time parents of a school shooter have been prosecuted.
RELATED: Oxford High School shooting suspect Ethan Crumbley appeals life sentence
Three days after the Trump campaign announced the rally in Butler, a western Pennsylvania town about an hour from Crook's home, Crooks made numerous searches online for well-known political figures and political events. He searched for the date and location of the Democratic National Convention, which takes place in August in Chicago, and for the location of the Trump rally. He also searched for information on Trump, Biden and other major political figures.
On the day of the rally, Crooks made several internet searches, including for photos of the location of Trump's speech and for a local gun store not far from his home, where he purchased bullets that day.
Investigators have found data showing that Crooks had visited the location of the rally a week before it was to be held. And on the morning of the rally, he visited the farm where the rally was to be held for over an hour. He then went home, and investigators believe he retrieved an AR-15 rifle owned by his father. Crooks' father told investigators that he saw his son leave the home with the rifle and believed he was going to a shooting range that the two had frequented.
On the day of the rally, his parents attempted to reach out to Crooks to find him. He didn't respond.