The FBI on Monday morning told reporters that would-be Trump assassin Thomas Crooks accessed the roof of a building near former President Trump’s July 13 rally in Butler, Pennsylvania, by climbing up HVAC equipment and piping.

Crooks then traversed multiple rooftops before he found his shooting position on top of a building owned by American Glass Research (AGR), located near the Butler Farm Show fairgrounds about 150 yards from where the former president spoke at his rally.

The FBI hosted a press conference call with reporters more than two weeks after 20-year-old Crooks fired at Trump with a DPMS AR-15-style firearm with a collapsable stock during the rally in an assassination attempt that nicked the president’s ear but left one man dead and two others hospitalized with gunshot wounds.

While investigators determined that Crooks did purchase a ladder just hours prior to the assassination attempt, he left it at his residence in Bethel Park and did not use the ladder at the rally later on.

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Kevin Rojek, special agent in charge at the FBI’s Pittsburgh field office, said the agency has examined more than 2,100 tips related to the assassination attempt since July 13.

Leading up to the shooting, Crooks apparently conducted internet searches for current and former presidents. 

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The Trump campaign announced the Butler rally on July 3, and three days later, Crooks signed up for the event. That same day — July 6 — he researched how far Lee Henry Oswald was from the late President John F. Kennedy when Oswald assassinated the former president in 1963. On July 7, he traveled to the rally site and spent approximately 20 minutes in the area, Rojek said.

Pictures of Thomas Mathew Crooks taken by a sniper. (Sen. Ron Johnson’s Office)

Crooks’ interest in firearms began around 2023, when he began taking shooting lessons. He made 25 online firearms purchases using an alias in the spring of 2023. 

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“Throughout the first half of 2024, a subject made six chemical precursor related purchases online of materials used to create the explosive devices recovered in the subject’s vehicle and home. And again for those purchases, he used aliases,” Rojek said.

Blood is seen in the stands after guns were fired at Republican candidate Donald Trump at a campaign event at Butler Farm Show Inc. in Butler, Pennsylvania, July 13, 2024. The suspected shooter who wounded Republican presidential candidate Donald Trump at a rally is dead, US media reported Saturday, along with one bystander.  (Rebecca Droke/AFP via Getty Images)

Crook’s father legally purchased the AR-15-style rifle Crooks used at the rally, and he legally transferred it to his son. He also legally purchased 50 rounds of ammunition from a local gun store on the morning of the rally, according to the FBI. 

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On the day of the rally, Crooks parked his vehicle and flew a drone between about 3:50 p.m. and 4 p.m. about 200 yards from where the former president would be speaking on July 13. FBI Director Christopher Wray testified during a July 17 congressional hearing that Crooks had been at the rally site for about 70 minutes the morning of the assassination attempt. 

Law enforcement officers move during a rally on July 13, 2024 in Butler, Pennsylvania.  (Anna Moneymaker/Getty Images)

It is still unclear how Crooks evaded security even after being noticed by law enforcement more than an hour before shots rang out, but the FBI said more than 300 agents and staff are working “round the clock” to gather facts and put together a clearer timeline of Crooks’ actions. 

Investigators located eight rounds on the roof where Crooks fired from, the agency said during the call.

An undated image of Thomas Matthew Crooks.  (Handout via AFP)

Law enforcement first reported seeing a suspicious person near the rally site around 5:10 p.m. on July 13 — an hour and one minute before Crooks began shooting. Local law enforcement notified command about the suspicious person and received confirmation that the Secret Service was aware of his presence.

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Over the next hour, law enforcement identified a building of interest, and snipers took photos of Crooks and his bicycle left near the rally grounds. Republican Missouri Sen. Josh Hawley, who was briefed on the assassination attempt, previously told Fox News Digital that a sniper “had eyes on” the suspicious person about 20 minutes before Crooks began firing.

FBI agents canvas Thomas Matthew Crooks’ neighborhood in Bethel Park, Pennsylvania on Monday, July 15, 2024. Crooks was killed on July 13 after attempting to assassinate former President Donald Trump at a campaign rally in Butler, Pennsylvania. (Derek Shook for Fox News Digital )

Trump took the podium around 6 p.m. — an hour after he was scheduled to speak. Eleven minutes later, Crooks fired multiple rounds, killing 50-year-old Corey Comperatore and seriously wounding 57-year-old David Dutch and 74-year-old James Copenhaver. Dutch was hospitalized and has since been released, while Copenhaver remains hospitalized.

FBI officials are still working to determine Crooks’ motive behind the assassination attempt that rocked Butler and neighboring townships. They are also still working to determine whether Crooks planned with any coconspirators, though the agency clarified on Monday that there are no signs to indicate there were others involved.

“His primary social circle appears to be limited to his immediate family, as we believe he had few friends and acquaintances throughout his life.”

— Kevin Rojek, special agent in charge, FBI Pittsurgh field office

The FBI’s Behavioral Analysis Unit is also working to build out a more comprehensive profile for Crooks. 

The Butler Farm Show, site of a campaign rally for Republican presidential candidate former President Donald Trump, is seen Monday July 15, 2024 in Butler, Pa. Trump was wounded on July 13 during an assassination attempt while speaking at the rally.  (AP Photo/Gene J. Puskar)

“Investigators have interviewed dozens of people who knew or interacted with the subject. This included family members, coworkers, former teachers, classmates, and others,” Rojek said. “We also consulted with specialists assigned to the FBI’s Behavioral Analysis Unit to offer their expertise as we work to develop a profile of the subject. We have learned the subject was highly intelligent, attended college and maintained steady employment.”

Rojek later on described Crooks as a “loner, as far as his association or any other activities related to his mental state.”

Trump is expected to return to Butler at some point for another rally, but he has not released any details on when that will be.

Yun said that the department’s current system is unable to track what medical conditions are complicated by a heat related illness. However, emergency room doctors at hospitals in the greater Boston area told the Globe that the number of patients with heat-related complications rose during the heat waves this summer.

“The difference this year is that the heat wave has been earlier in the season,” said Scott Goldberg, director of EMS at Massachusetts General Brigham. “We’re generally not seeing this type of extreme heat for such a long period of time.”

A Globe analysis of EMS calls during the heat waves this summer shows that there were more calls when it was hotter outside. During the recent heat wave on the week of July 15, EMS calls were 6 percent to 21.6 percent above the daily call volume.

This was a consistent trend over the past four years. During a four-day heatwave that began on June 5, 2021, which EMS said was comparable to the one two weeks ago, calls were about 30 percent to 43 percent above the average daily volume.

Center for Disease Control data also shows that emergency room admission for heat related illnesses picked up this summer compared to previous months this year.

According to the CDC Heat and Health tracker, a heat wave is defined as temperatures of 90 degrees and above each day for two days or more.

A threshold for declaring a heat emergency is a consecutive two days or more of 95 degree or higher heat index. The heat index takes into account both the temperature and relative humidity, which is a marker of how hot it feels outside. According to the National Weather Service, the heat index was 94 F at 12:45 p.m. on Thursday, the most current data available.

“When we’re hitting heat indexes above 90-95, it really does become dangerous,” said Yun.

The problem is poised to intensify.

“Heat waves are unquestionably getting worse and will continue getting worse due to emissions,” said Mathew Barlow, a University of Massachusetts Lowell environmental Earth and atmospheric sciences professor.

Barlow says this heat is not a new normal, because we shouldn’t expect it to stay the same; instead, the next several years will be getting hotter.

Doctors are worried because the rising heat affects some of the region’s most vulnerable people such as the elderly and people with chronic medical conditions. Older people, who may have long term medical problems or take medications, need to be extra cautious with the intense heat, they said.

Some populations are at a higher risk of heat illness than others. There are those who are unable to limit their heat exposure such as outdoor workers, military personnel or unhoused people.

The lasting effects of heat are also known to impact those who do not have proper air conditioning, which represents about 5.5 percent of Boston households, according to a Boston Globe analysis of Census data.

Traditionally vulnerable low-income households are more affected by the heat waves because they often live in homes that are not energy-efficient and are expensive to cool. This “energy insecurity” makes it hard to stay comfortable and healthy during extreme heat, according to the US Environmental Protection Agency.

Heat has been rising across the country in the past decades. Major cities have been encountering heat waves more frequently, according to the agency. The average amount of annual heat waves rose from two a year during the 1960s to six a year during the 2010s and 2020s.

As heat waves become more common due to climate change, Massachusetts sits in an uncomfortable position where days will continue to be over 90 F during the summer. The populated urban areas with little tree coverage and open green space makes the region feel hotter.

There are predictions by the Massachusetts Department of Health Bureau of Climate and Environmental Health that by 2050 there will be a 10 to 28 day increase in extreme heat.

“I’m worried that 10 to 15 years from now, we might be looking back in 2024 and say this was actually one of the coolest summers,” said Yun.

Warmer temperatures lead to more hospitalizations for health issues such as heart disease and heat exhaustion. If heat exhaustion isn’t treated, it can turn into heat stroke, which can cause serious illness, brain damage and death.

In severe cases, the heat waves can cause deaths. Even heat-related deaths have been rising in the U.S., with about 1,602 in 2021, 1,722 in 2022, and 2,302 in 2023.

Dr. Tess Wiskel, an emergency physician at Beth Israel Deaconess Medical Center, said the center saw more heat-related illnesses during the July 15 heat wave than in previous ones this summer.

“There’s no question that it’s adding to the burden of care that we need to give in the emergency department,” she said.

Some doctors say they have experience with burnout and feeling stressed but not more than usual due to the ongoing issue of understaffing at ERs.

When temperatures reach high 80s and 90s, the Boston Public Health Commission recommends people to stay in air-conditioned spaces and limit outdoor activities.

“During heat emergencies, cooling centers are available for vulnerable residents. All Boston residents are encouraged to stay hydrated and check in on their neighbors,” said Dr. Bisola Ojikutu, executive director of the Boston Public Health Commission.

Rachel Umansky-Castro can be reached at rachel.umanskycastro@globe.com.