Trump shooting updates: Shooter flew drone near site hours before shooting

House Oversight Committee Chairman James Comer has subpoenaed Secret Service Director Kim Cheatle to ensure she appears at the Oversight hearing planned for Monday, July 22.

In the days since the attack, Cheatle and the Secret Service have faced heightening scrutiny for failing to prevent the incident from happening, and even calls from some to resign. Cheatle said she would not resign from her role.

-ABC News’ Will Steakin and Lauren Peller

Investigators have found that Thomas Matthew Crooks, the 20-year-old gunman, was a loner without friends and was described as "odd," according to multiple sources briefed on the investigation.

Crooks had been "bullied" a little, "but not over the top," one source said.

Analysts are trying to assess whether he was hard to get close to or was shut off because he was hiding something, sources said.

Investigators haven’t found any helpful information on Crooks’ phone or computer and are looking to see if he may have used "burners" or other devices, sources said.

-ABC News’ Pierre Thomas and Josh Margolin

Minutes before the shooting, gunman Thomas Matthew Crooks was seen walking around near the magnetometers and people reported him as suspicious, according to law enforcement sources.

When someone in law enforcement started to approach Crooks, the 20-year-old backed up and faded into the crowd, according to sources.

Crooks then climbed on top of air conditioning units and pulled himself up to the roof of the building beside those units, sources said.

Once on the roof of that first building, he worked his way toward another taller, adjacent building that gave him the vantage point to fire in Donald Trump’s direction, sources said. He jumped and landed where he wanted to be and slowly made his way to the summit of the sloped building, sources said.

Secret Service agents heard radio traffic about a suspicious person and later heard another radio dispatch about some sort of confrontation with police, sources said.

When bystanders noticed Crooks, an officer climbed up, sources said. Crooks pointed his gun at the officer who fell to the ground, sources said.

There were police personnel and snipers from the local countersniper units in the building where Crooks eventually took up a position to fire at Trump, sources said. Investigators believe that could have led to confusion as Secret Service snipers were trying to determine whether there was a threat to Trump and where it might be coming from.

The Secret Service sharpshooters knew that building was being used by law enforcement and, investigators believe, that might have led to a split-second delay in reacting as the Secret Service snipers had to figure out whether the man on the roof was an officer or a suspect, sources said.

-ABC News’ Luke Barr, Jack Date, Pierre Thomas, Josh Margolin and Aaron Katersky

House Speaker Mike Johnson said Wednesday that the House will set up a bipartisan task force to investigate the shooting when the House returns from recess.

"I will set up on Monday a task force, special task force within the House. The reason we'll do it that way is because it's a more precision strike, it goes quicker," Johnson told Fox News. "There is not a lot of procedural hurdles and we’ll have subpoena authority with the task force, as well. It will be compiled of Republicans and Democrats to get down to the bottom of this quickly so the American people can get the answers they deserve."

The speaker also said he will call on Secret Service Director Kim Cheatle to resign.

-ABC News’ Lauren Peller